Golf ball

ABSTRACT

A golf ball  2  includes a core  4 , a mid layer  6 , a cover  8 , and dimples  10 . A Shore C hardness Hmc of the mid layer  6  is greater than a Shore C hardness Hs at a surface of the core  4 . A Shore D hardness He of the cover  8  is less than a Shore D hardness Hm of the mid layer  6 . Peak values and orders of maximum peaks of data constellations of the golf ball  2  are calculated. A minimum value of the peak values is not less than 95 mm. A minimum value of the orders is not less than 27, and a maximum value of the orders is not greater than 37. An average of the orders is not less than 30 and not greater than 34.

This application claims priority on Patent Application No. 2016-246079filed in JAPAN on Dec. 20, 2016. The entire contents of this JapanesePatent Application are hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to golf balls. Specifically, the presentinvention relates to golf balls including a core, a mid layer, a cover,and dimples.

Description of the Related Art

The face of a golf club has a loft angle. When a golf ball is hit withthe golf club, backspin due to the loft angle occurs in the golf ball.The golf ball flies with the backspin.

When a backspin rate is high, the run of the golf ball after landing isshort. By using a golf ball having a high backspin rate, a golf playercan cause the golf ball to stop at a target point. When a sidespin rateis high, the golf ball tends to curve. By using a golf ball having ahigh sidespin rate, a golf player can intentionally cause the golf ballto curve. A golf ball to which backspin is easily provided has excellentcontrollability. Golf players particularly place importance oncontrollability upon approach shots.

Golf balls have a large number of dimples on the surfaces thereof. Thedimples disturb the air flow around the golf ball during flight to causeturbulent flow separation. This phenomenon is referred to as“turbulization”. Due to the turbulization, separation points of the airfrom the golf ball shift backwards leading to a reduction of drag. Theturbulization promotes the displacement between the separation point onthe upper side and the separation point on the lower side of the golfball, which results from the backspin, thereby enhancing the lift forcethat acts upon the golf ball. The reduction of drag and the enhancementof lift force are referred to as a “dimple effect”. Excellent dimplesefficiently disturb the air flow. The excellent dimples produce a longflight distance.

There have been various proposals for dimples. JPH4-109968 discloses agolf ball in which the dimple pattern of each hemisphere can be dividedinto six units. JP2004-243124 (US2004/0157682) discloses a golf ball inwhich the dimple pattern near each pole can be divided into four unitsand the dimple pattern near the equator can be divided into five units.JP2011-10667 (US2010/0326175) discloses a golf ball in which a parameterdependent on the shapes of dimples falls within a predetermined range.

In recent years, golf players' requirements for golf balls have beenescalated. There is room for improvement in various performancecharacteristics of golf balls.

An object of the present invention is to provide a golf ball havingexcellent flight performance and excellent controllability upon anapproach shot.

SUMMARY OF THE INVENTION

A golf ball according to the present invention includes a core, a midlayer positioned outside the core, and a cover positioned outside themid layer. A Shore C hardness Hmc of the mid layer is greater than aShore C hardness Hs at a surface of the core. A Shore D hardness He ofthe cover is less than a Shore D hardness Hm of the mid layer. The golfball further includes a plurality of dimples on a surface thereof. Aminimum value of 15 peak values obtained by executing steps (a) to (h)for each of 15 axes Ax is not less than 95 mm, when spherical polarcoordinates of a point that is located on a surface of a phantom sphereof the golf ball and has a latitude of θ (degrees) and a longitude of ϕ(degrees) are represented by (θ, ϕ), the 15 axes Ax being

(1) a first axis Ax1 passing through a point Pn1 coordinates of whichare (75, 270) and a point Ps1 coordinates of which are (−75, 90),

(2) a second axis Ax2 passing through a point Pn2 coordinates of whichare (60, 270) and a point Ps2 coordinates of which are (−60, 90)

(3) a third axis Ax3 passing through a point Pn3 coordinates of whichare (45, 270) and a point Ps3 coordinates of which are (−45, 90),

(4) a fourth axis Ax4 passing through a point Pn4 coordinates of whichare (30, 270) and a point Ps4 coordinates of which are (−30, 90),

(5) a fifth axis Ax5 passing through a point Pn5 coordinates of whichare (15, 270) and a point Ps5 coordinates of which are (−15, 90),

(6) a sixth axis Ax6 passing through a point Pn6 coordinates of whichare (75, 0) and a point Ps6 coordinates of which are (−75, 180),

(7) a seventh axis Ax7 passing through a point Pn7 coordinates of whichare (60, 0) and a point Ps7 coordinates of which are (−60, 180),

(8) an eighth axis Ax8 passing through a point Pn8 coordinates of whichare (45, 0) and a point Ps8 coordinates of which are (−45, 180),

(9) a ninth axis Ax9 passing through a point Pn9 coordinates of whichare (30, 0) and a point Ps9 coordinates of which are (−30, 180),

(10) a tenth axis Ax10 passing through a point Pn10 coordinates of whichare (15, 0) and a point Ps10 coordinates of which are (−15, 180),

(11) an eleventh axis Ax11 passing through a point Pn11 coordinates ofwhich are (75, 90) and a point Ps11 coordinates of which are (−75, 270),

(12) a twelfth axis Ax12 passing through a point Pn12 coordinates ofwhich are (60, 90) and a point Ps12 coordinates of which are (−60, 270),

(13) a thirteenth axis Ax13 passing through a point Pn13 coordinates ofwhich are (45, 90) and a point Ps13 coordinates of which are (−45, 270),

(14) a fourteenth axis Ax14 passing through a point Pn14 coordinates ofwhich are (30, 90) and a point Ps14 coordinates of which are (−30, 270),and

(15) a fifteenth axis Ax15 passing through a point Pn15 coordinates ofwhich are (15, 90) and a point Ps15 coordinates of which are (−15, 270),the steps (a) to (h) being the steps of

(a) assuming a great circle that is present on the surface of thephantom sphere and is orthogonal to the axis Ax,

(b) assuming two small circles that are present on the surface of thephantom sphere, that are orthogonal to the axis Ax, and of whichabsolute values of central angles with the great circle are each 30°,

(c) defining a region, of the surface of the golf ball, which isobtained by dividing the surface of the golf ball at these small circlesand which is sandwiched between these small circles,

(d) determining 30240 points, on the region, arranged at intervals of acentral angle of 3° in a direction of the axis Ax and at intervals of acentral angle of 0.25° in a direction of rotation about the axis Ax,

(e) calculating a length L1 of a perpendicular line that extends fromeach point to the axis Ax,

(f) calculating a total length L2 by summing 21 lengths L1 calculated onthe basis of 21 perpendicular lines arranged in the direction of theaxis Ax, (g) obtaining a transformed data constellation by performingFourier transformation on a data constellation of 1440 total lengths L2calculated along the direction of rotation about the axis Ax, and

(h) calculating a peak value and an order of a maximum peak of thetransformed data constellation.

A minimum value of 15 orders obtained by executing the steps (a) to (h)is not less than 27. A maximum value of the 15 orders obtained byexecuting the steps (a) to (h) is not greater than 37. An average of the15 orders obtained by executing the steps (a) to (h) is not less than 30and not greater than 34.

The dimple pattern of the golf ball according to the present inventionhas an excellent aerodynamic characteristic. The golf ball has excellentflight performance. When the golf ball is hit with a short iron, thespin rate is high. The golf ball has excellent controllability upon anapproach shot. The golf ball achieves both desired flight performanceand desired controllability.

Preferably, an average of the 15 peak values obtained by executing thesteps (a) to (h) is not less than 200 mm.

Preferably, a total volume of the dimples is not less than 450 mm³ andnot greater than 750 mm³.

Preferably, a difference DH in Shore C hardness between the surface anda central point of the core, a thickness Tm (mm) and the Shore Dhardness Hm of the mid layer, a thickness Tc (mm) and the Shore Dhardness He of the cover, and an amount of compressive deformation Sb(mm) of the golf ball satisfy the following mathematical formulas (i)and (ii).

(DH*Hm)/(Hc*Tc)>90  (i)

((Sb*Tc)/(Hc*Hm*Tm))*1000>0.60  (ii)

Preferably, a difference (Hmc−Hs) between the Shore C hardness Hmc ofthe mid layer and the Shore C hardness Hs at the surface of the core isnot less than 5.

Preferably, a difference (Hm−Hc) between the Shore D hardness Hm of themid layer and the Shore D hardness He of the cover is not less than 20.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a golf ball according toan embodiment of the present invention;

FIG. 2 is an enlarged front view of the golf ball in FIG. 1;

FIG. 3 is a plan view of the golf ball in FIG. 2;

FIG. 4 is a partially enlarged cross-sectional view of the golf ball inFIG. 1;

FIG. 5 is a schematic diagram for explaining an evaluation method forthe golf ball in FIG. 2;

FIG. 6 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 7 is a schematic cross-sectional view for explaining the evaluationmethod for the golf ball in FIG. 2;

FIG. 8 is a schematic cross-sectional view for explaining the evaluationmethod for the golf ball in FIG. 2;

FIG. 9 is a graph showing an evaluation result of the golf ball in FIG.2;

FIG. 10 is a graph showing another evaluation result of the golf ball inFIG. 2;

FIG. 11 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 12 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 13 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 14 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 15 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 16 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 17 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 18 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 19 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 20 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 21 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 22 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 23 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 24 is a schematic diagram for explaining the evaluation method forthe golf ball in FIG. 2;

FIG. 25 is a front view of a golf ball according to Example 2 of thepresent invention;

FIG. 26 is a plan view of the golf ball in FIG. 25;

FIG. 27 is a front view of a golf ball according to Example 3 of thepresent invention;

FIG. 28 is a plan view of the golf ball in FIG. 27;

FIG. 29 is a front view of a golf ball according to Comparative Example1;

FIG. 30 is a plan view of the golf ball in FIG. 29;

FIG. 31 is a front view of a golf ball according to Comparative Example2;

FIG. 32 is a plan view of the golf ball in FIG. 31;

FIG. 33 is a front view of a golf ball according to Comparative Example3;

FIG. 34 is a plan view of the golf ball in FIG. 33;

FIG. 35 is a front view of a golf ball according to Comparative Example4; and

FIG. 36 is a plan view of the golf ball in FIG. 35.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe in detail the present invention based onpreferred embodiments with appropriate reference to the drawings.

A golf ball 2 shown in FIG. 1 includes a spherical core 4, a mid layer 6positioned outside the core 4, and a cover 8 positioned outside the midlayer 6. The golf ball 2 has a plurality of dimples 10 on the surfacethereof. Of the surface of the golf ball 2, a part other than thedimples 10 is a land 12. The golf ball 2 includes a paint layer and amark layer on the external side of the cover 8 although these layers arenot shown in the drawing. The golf ball 2 may include another layerbetween the core 4 and the mid layer 6. The golf ball 2 may includeanother layer between the mid layer 6 and the cover 8.

The golf ball 2 preferably has a diameter of not less than 40 mm and notgreater than 45 mm. From the viewpoint of conformity to the rulesestablished by the United States Golf Association (USGA), the diameteris particularly preferably not less than 42.67 mm. In light ofsuppression of air resistance, the diameter is more preferably notgreater than 44 mm and particularly preferably not greater than 42.80mm. The golf ball 2 preferably has a weight of not less than 40 g andnot greater than 50 g. In light of attainment of great inertia, theweight is more preferably not less than 44 g and particularly preferablynot less than 45.00 g. From the viewpoint of conformity to the rulesestablished by the USGA, the weight is particularly preferably notgreater than 45.93 g.

The core 4 is formed by crosslinking a rubber composition. Examples ofpreferable base rubbers for use in the rubber composition includepolybutadienes, polyisoprenes, styrene-butadiene copolymers,ethylene-propylene-diene copolymers, and natural rubbers. In light ofresilience performance, polybutadienes are preferable. When apolybutadiene and another rubber are used in combination, it ispreferred if the polybutadiene is a principal component. Specifically,the proportion of the polybutadiene to the entire base rubber ispreferably not less than 50% by weight and particularly preferably notless than 80% by weight. A polybutadiene in which the proportion ofcis-1,4 bonds is not less than 80% is particularly preferable.

The rubber composition of the core 4 preferably includes aco-crosslinking agent. Preferable co-crosslinking agents in light ofresilience performance are monovalent or bivalent metal salts of anα,β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Examples ofpreferable co-crosslinking agents include zinc acrylate, magnesiumacrylate, zinc methacrylate, and magnesium methacrylate. In light ofresilience performance, zinc acrylate and zinc methacrylate areparticularly preferable.

The rubber composition may include a metal oxide and an α,β-unsaturatedcarboxylic acid having 2 to 8 carbon atoms. They both react with eachother in the rubber composition to obtain a salt. The salt serves as aco-crosslinking agent. Examples of preferable α,β-unsaturated carboxylicacids include acrylic acid and methacrylic acid. Examples of preferablemetal oxides include zinc oxide and magnesium oxide.

In light of resilience performance of the golf ball 2, the amount of theco-crosslinking agent per 100 parts by weight of the base rubber ispreferably not less than 10 parts by weight and particularly preferablynot less than 15 parts by weight. In light of soft feel at impact, theamount is preferably not greater than 50 parts by weight andparticularly preferably not greater than 45 parts by weight.

Preferably, the rubber composition of the core 4 includes an organicperoxide. The organic peroxide serves as a crosslinking initiator. Theorganic peroxide contributes to the resilience performance of the golfball 2. Examples of suitable organic peroxides include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Anorganic peroxide with particularly high versatility is dicumyl peroxide.

In light of resilience performance of the golf ball 2, the amount of theorganic peroxide per 100 parts by weight of the base rubber ispreferably not less than 0.1 parts by weight, more preferably not lessthan 0.3 parts by weight, and particularly preferably not less than 0.5parts by weight. In light of soft feel at impact, the amount ispreferably not greater than 3.0 parts by weight, more preferably notgreater than 2.8 parts by weight, and particularly preferably notgreater than 2.5 parts by weight.

Preferably, the rubber composition of the core 4 includes an organicsulfur compound. Organic sulfur compounds include naphthalenethiolcompounds, benzenethiol compounds, and disulfide compounds.

Examples of naphthalenethiol compounds include 1-naphthalenethiol,2-naphthalenethiol, 4-chloro-1-naphthalenethiol,4-bromo-1-naphthalenethiol, 1-chloro-2-naphthalenethiol,l-bromo-2-naphthalenethiol, l-fluoro-2-naphthalenethiol,l-cyano-2-naphthalenethiol, and 1-acetyl-2-naphthalenethiol.

Examples of benzenethiol compounds include benzenethiol,4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol,3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol,2,5-dichlorobenzenethiol, 3,5-dichlorobenzenethiol,2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol,3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol,2,4,6-trichlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol,2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol,2-cyanobenzenethiol, 4-nitrobenzenethiol, and 2-nitrobenzenethiol.

Examples of disulfide compounds include diphenyl disulfide,bis(4-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide,bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide,bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide,bis(4-cyanophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide,bis(3,5-dichlorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide,bis(2,5-dibromophenyl)disulfide, bis(3,5-dibromophenyl)disulfide,bis(2-chloro-5-bromophenyl)disulfide,bis(2-cyano-5-bromophenyl)disulfide,bis(2,4,6-trichlorophenyl)disulfide,bis(2-cyano-4-chloro-6-bromophenyl)disulfide,bis(2,3,5,6-tetrachlorophenyl)disulfide,bis(2,3,4,5,6-pentachlorophenyl)disulfide, andbis(2,3,4,5,6-pentabromophenyl)disulfide.

In light of resilience performance of the golf ball 2, the amount of theorganic sulfur compound per 100 parts by weight of the base rubber ispreferably not less than 0.1 parts by weight and particularly preferablynot less than 0.2 parts by weight. In light of soft feel at impact, theamount is preferably not greater than 1.5 parts by weight, morepreferably not greater than 1.0 parts by weight, and particularlypreferably not greater than 0.8 parts by weight. Two or more organicsulfur compounds may be used in combination. A naphthalenethiol compoundand a disulfide compound are preferably used in combination.

Preferably, the rubber composition of the core 4 includes a carboxylicacid or a carboxylate. The core 4 including a carboxylic acid or acarboxylate has a low hardness around the central point thereof. Thecore 4 has an outer-hard/inner-soft structure. When the golf ball 2including the core 4 is hit with a golf club, the spin rate is low. Withthe golf ball 2 having a low spin rate, a large flight distance isobtained. Examples of preferable carboxylic acids include benzoic acid.Examples of preferable carboxylates include zinc octoate and zincstearate. The rubber composition particularly preferably includesbenzoic acid. The total amount of the carboxylic acid and thecarboxylate per 100 parts by weight of the base rubber is preferably notless than 1 parts by weight and not greater than 20 parts by weight.

The rubber composition of the core 4 may include a filler for thepurpose of specific gravity adjustment and the like. Examples ofsuitable fillers include zinc oxide, barium sulfate, calcium carbonate,and magnesium carbonate. The amount of the filler is determined asappropriate so that the intended specific gravity of the core 4 isaccomplished. The rubber composition may include various additives, suchas sulfur, an anti-aging agent, a coloring agent, a plasticizer, adispersant, and the like, in an adequate amount. The rubber compositionmay include crosslinked rubber powder or synthetic resin powder.

The core 4 preferably has a diameter of not less than 38.0 mm. The golfball 2 including the core 4 having a diameter of not less than 38.0 mmhas excellent resilience performance. From this viewpoint, the diameteris more preferably not less than 38.5 mm and particularly preferably notless than 39.5 mm. From the viewpoint that the mid layer 6 and the cover8 can have sufficient thicknesses, the diameter is preferably notgreater than 41.0 mm and particularly preferably not greater than 40.5mm.

The core 4 has a weight of preferably not less than 10 g and not greaterthan 40 g. The temperature for crosslinking the core 4 is not lower than140° C. and not higher than 180° C. The time period for crosslinking thecore 4 is not shorter than 10 minutes and not longer than 60 minutes.The core 4 may include a center and an envelope layer. The core 4 mayhave three or more layers. The core 4 may have a rib on the surfacethereof. The core 4 may be hollow.

The difference DH between a hardness Hs at the surface of the core 4 anda hardness Ho at the central point of the core 4 is preferably not lessthan 15. The core 4 in which the difference DH is not less than 15 has aso-called outer-hard/inner-soft structure. When the golf ball 2including the core 4 is hit with a driver, the spin is suppressed. Whenthe golf ball 2 including the core 4 is hit with a driver, a high launchangle is obtained.

Upon a shot with a driver, an appropriate trajectory height andappropriate flight duration are required. With the golf ball 2 thatachieves a desired trajectory height and desired flight duration at ahigh spin rate, the run after landing is short. With the golf ball 2that achieves a desired trajectory height and desired flight duration ata high launch angle, the run after landing is long. In light of flightdistance, the golf ball 2 that achieves a desired trajectory height anddesired flight duration at a high launch angle is preferable. The core 4having an outer-hard/inner-soft structure can contribute to a highlaunch angle and a low spin rate as described above. The golf ball 2including the core 4 has excellent flight performance.

In light of flight performance, the difference DH is preferably not lessthan 20 and particularly preferably not less than 25. In light of easeof producing the core 4, the difference DH is preferably not greaterthan 50 and particularly preferably not greater than 45.

In light of resilience performance, the central hardness Ho ispreferably not less than 30, more preferably not less than 35, andparticularly preferably not less than 40. In light of spin suppressionand feel at impact, the hardness Ho is preferably not greater than 70,more preferably not greater than 65, and particularly preferably notgreater than 60.

The hardness Ho is measured with a Shore C type hardness scale mountedto an automated hardness meter (trade name “digi test II” manufacturedby Heinrich Bareiss Prüfgerätebau GmbH). The hardness scale is pressedagainst the central point of the cross-section of a hemisphere obtainedby cutting the golf ball 2. The measurement is conducted in anenvironment of 23° C.

In light of spin suppression, the surface hardness Hs is preferably notless than 70, more preferably not less than 72, and particularlypreferably not less than 74. In light of durability of the golf ball 2,the hardness Hs is preferably not greater than 90, more preferably notgreater than 88, and particularly preferably not greater than 86.

The hardness Hs is measured with a Shore C type hardness scale mountedto an automated hardness meter (trade name “digi test II” manufacturedby Heinrich Bareiss Prüfgerätebau GmbH). The hardness scale is pressedagainst the surface of the core 4. The measurement is conducted in anenvironment of 23° C.

The mid layer 6 is positioned between the core 4 and the cover 8. Themid layer 6 is formed from a thermoplastic resin composition. Examplesof the base polymer of the resin composition include ionomer resins,thermoplastic polyester elastomers, thermoplastic polyamide elastomers,thermoplastic polyurethane elastomers, thermoplastic polyolefinelastomers, and thermoplastic polystyrene elastomers. Ionomer resins areparticularly preferable. Ionomer resins are highly elastic. The golfball 2 that includes the mid layer 6 including an ionomer resin hasexcellent resilience performance.

An ionomer resin and another resin may be used in combination. In thiscase, in light of resilience performance, the ionomer resin is includedas the principal component of the base polymer. The proportion of theionomer resin to the entire base polymer is preferably not less than 50%by weight, more preferably not less than 70% by weight, and particularlypreferably not less than 85% by weight.

Examples of preferable ionomer resins include binary copolymers formedwith an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8carbon atoms. A preferable binary copolymer includes 80% by weight ormore but 90% by weight or less of an α-olefin, and 10% by weight or morebut 20% by weight or less of an α,β-unsaturated carboxylic acid. Thebinary copolymer has excellent resilience performance. Examples of otherpreferable ionomer resins include ternary copolymers formed with: anα-olefin; an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms;and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. Apreferable ternary copolymer includes 70% by weight or more but 85% byweight or less of an α-olefin, 5% by weight or more but 30% by weight orless of an α,β-unsaturated carboxylic acid, and 1% by weight or more but25% by weight or less of an α,β-unsaturated carboxylate ester. Theternary copolymer has excellent resilience performance. For the binarycopolymer and the ternary copolymer, preferable α-olefins are ethyleneand propylene, while preferable α,β-unsaturated carboxylic acids areacrylic acid and methacrylic acid. A particularly preferable ionomerresin is a copolymer formed with ethylene and acrylic acid. Anotherparticularly preferable ionomer resin is a copolymer formed withethylene and methacrylic acid.

In the binary copolymer and the ternary copolymer, some of the carboxylgroups are neutralized with metal ions. Examples of metal ions for usein neutralization include sodium ion, potassium ion, lithium ion, zincion, calcium ion, magnesium ion, aluminum ion, and neodymium ion. Theneutralization may be carried out with two or more types of metal ions.Particularly suitable metal ions in light of resilience performance anddurability of the golf ball 2 are sodium ion, zinc ion, lithium ion, andmagnesium ion.

Specific examples of ionomer resins include trade names “Himilan 1555”,“Himilan 1557”, “Himilan 1605”, “Himilan 1706”, “Himilan 1707”, “Himilan1856”, “Himilan 1855”, “Himilan AM7311”, “Himilan AM7315”, “HimilanAM7317”, “Himilan AM7329”, and “Himilan AM7337”, manufactured by DuPont-MITSUI POLYCHEMICALS Co., Ltd.; trade names “Surlyn 6120”, “Surlyn6910”, “Surlyn 7930”, “Surlyn 7940”, “Surlyn 8140”, “Surlyn 8150”,“Surlyn 8940”, “Surlyn 8945”, “Surlyn 9120”, “Surlyn 9150”, “Surlyn9910”, “Surlyn 9945”, “Surlyn AD8546”, “HPF1000”, and “HPF2000”,manufactured by E.I. du Pont de Nemours and Company; and trade names“IOTEK 7010”, “IOTEK 7030”, “IOTEK 7510”, “IOTEK 7520”, “IOTEK 8000”,and “IOTEK 8030”, manufactured by ExxonMobil Chemical Corporation. Twoor more ionomer resins may be used in combination.

The resin composition of the mid layer 6 may include a styreneblock-containing thermoplastic elastomer. The styrene block-containingthermoplastic elastomer includes a polystyrene block as a hard segment,and a soft segment. A typical soft segment is a diene block. Examples ofcompounds for the diene block include butadiene, isoprene,1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isopreneare preferable. Two or more compounds may be used in combination.

Examples of styrene block-containing thermoplastic elastomers includestyrene-butadiene-styrene block copolymers (SBS),styrene-isoprene-styrene block copolymers (SIS),styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenatedSBS, hydrogenated SIS, and hydrogenated SIBS. Examples of hydrogenatedSBS include styrene-ethylene-butylene-styrene block copolymers (SEBS).Examples of hydrogenated SIS include styrene-ethylene-propylene-styreneblock copolymers (SEPS). Examples of hydrogenated SIBS includestyrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS).

In light of resilience performance of the golf ball 2, the content ofthe styrene component in the styrene block-containing thermoplasticelastomer is preferably not less than 10% by weight, more preferably notless than 12% by weight, and particularly preferably not less than 15%by weight. In light of feel at impact of the golf ball 2, the content ispreferably not greater than 50% by weight, more preferably not greaterthan 47% by weight, and particularly preferably not greater than 45% byweight.

In the present invention, styrene block-containing thermoplasticelastomers include an alloy of an olefin and one or more membersselected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, andSEEPS. The olefin component in the alloy is presumed to contribute toimprovement of compatibility with another base polymer. The alloy cancontribute to the resilience performance of the golf ball 2. An olefinhaving 2 to 10 carbon atoms is preferable. Examples of suitable olefinsinclude ethylene, propylene, butene, and pentene. Ethylene and propyleneare particularly preferable.

Specific examples of polymer alloys include trade names “RABALONT3221C”, “RABALON T3339C”, “RABALON SJ4400N”, “RABALON SJ5400N”,“RABALON SJ6400N”, “RABALON SJ7400N”, “RABALON SJ8400N”, “RABALONSJ9400N”, and “RABALON SR04”, manufactured by Mitsubishi ChemicalCorporation. Other specific examples of styrene block-containingthermoplastic elastomers include trade name “Epofriend A1010”manufactured by Daicel Chemical Industries, Ltd., and trade name “SEPTONHG-252” manufactured by Kuraray Co., Ltd.

In light of feel at impact, the proportion of the styreneblock-containing thermoplastic elastomer to the entire base polymer ispreferably not less than 1% by weight and particularly preferably notless than 2% by weight. In light of spin suppression, this proportion ispreferably not greater than 20% by weight, more preferably not greaterthan 15% by weight, and particularly preferably not greater than 10% byweight.

The resin composition of the mid layer 6 may include a filler for thepurpose of specific gravity adjustment and the like. Examples ofsuitable fillers include zinc oxide, barium sulfate, calcium carbonate,and magnesium carbonate. The resin composition may include powder of ametal with a high specific gravity. Specific examples of metals with ahigh specific gravity include tungsten and molybdenum. The amount of thefiller is determined as appropriate so that the intended specificgravity of the mid layer 6 is accomplished. The resin composition mayinclude a coloring agent, crosslinked rubber powder, or synthetic resinpowder. When the hue of the golf ball 2 is white, a typical coloringagent is titanium dioxide.

The mid layer 6 preferably has a hardness Hm of not less than 54. Withthe golf ball 2 including the mid layer 6 having a hardness Hm of notless than 54, a spin rate upon a shot with a driver is reduced. The midlayer 6 can contribute to the flight performance of the golf ball 2.From this viewpoint, the hardness Hm is more preferably not less than 57and particularly preferably not less than 60. In light of feel atimpact, the hardness Hm is preferably not greater than 80, morepreferably not greater than 75, and particularly preferably not greaterthan 72.

The hardness Hm of the mid layer 6 is measured according to thestandards of “ASTM-D 2240-68”. The hardness Hm is measured with a ShoreD type hardness scale mounted to an automated hardness meter (trade name“digi test II” manufactured by Heinrich Bareiss Prüfgerätebau GmbH). Forthe measurement, a sheet that is formed by hot press, is formed from thesame material as that of the mid layer 6, and has a thickness of about 2mm is used. Prior to the measurement, a sheet is kept at 23° C. for twoweeks. At the measurement, three sheets are stacked.

The mid layer 6 has a Shore C hardness Hmc of preferably not less than83, more preferably not less than 86, and particularly preferably notless than 90. The hardness Hmc is preferably not greater than 95.

The Shore C hardness Hmc of the mid layer 6 is measured with a Shore Ctype hardness scale mounted to an automated hardness meter (trade name“digi test II” manufactured by Heinrich Bareiss Prüfgerätebau GmbH). Forthe measurement, a sheet that is formed by hot press, is formed from thesame material as that of the mid layer 6, and has a thickness of about 2mm is used. Prior to the measurement, a sheet is kept at 23° C. for twoweeks. At the measurement, three sheets are stacked.

The mid layer 6 preferably has a thickness Tm of not less than 0.3 mmand not greater than 2.5 mm. With the golf ball 2 that includes the midlayer 6 having a thickness Tm of not less than 0.3 mm, spin upon a shotwith a driver is suppressed. From this viewpoint, the thickness Tm ismore preferably not less than 0.5 mm and particularly preferably notless than 0.8 mm. With the golf ball 2 that includes the mid layer 6having a thickness Tm of not greater than 2.5 mm, soft feel at impact isobtained. From this viewpoint, the thickness Tm is more preferably notgreater than 2.0 mm and particularly preferably not greater than 1.8 mm.The thickness Tm is measured at a position immediately below the land12.

The golf ball 2 may include two or more mid layers 6 positioned betweenthe core 4 and the cover 8. In this case, each mid layer 6 preferablyhas a thickness within the above range.

The cover 8 is the outermost layer except the mark layer and the paintlayer. The cover 8 is formed from a resin composition. Examples of thebase polymer of the resin composition include polyurethanes, ionomerresins, polyesters, polyamides, polyolefins, and polystyrenes. Apreferable base polymer in light of controllability upon an approachshot is a polyurethane. When a polyurethane and another resin are usedin combination for the cover 8, the proportion of the polyurethane tothe entire base resin is preferably not less than 50% by weight, morepreferably not less than 60% by weight, and particularly preferably notless than 70% by weight.

The resin composition of the cover 8 may include a thermoplasticpolyurethane or may include a thermosetting polyurethane. In light ofproductivity of the golf ball 2, the thermoplastic polyurethane ispreferable. The thermoplastic polyurethane includes a polyurethanecomponent as a hard segment, and a polyester component or a polyethercomponent as a soft segment. The thermoplastic polyurethane is flexible.The cover 8 in which the polyurethane is used has excellent scuffresistance.

The thermoplastic polyurethane has a urethane bond within the molecule.The urethane bond can be formed by reacting a polyol with apolyisocyanate. The polyol, as a material for the urethane bond, has aplurality of hydroxyl groups. Low-molecular-weight polyols andhigh-molecular-weight polyols can be used.

Examples of low-molecular-weight polyols include diols, triols,tetraols, and hexaols. Specific examples of diols include ethyleneglycol, diethylene glycol, triethylene glycol, 1,2-propanediol,1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol,2,3-dimethyl-2,3-butanediol, neopentyl glycol, pentanediol, hexanediol,heptanediol, octanediol, and 1,6-cyclohexanedimethylol. Aniline diols orbisphenol A diols may be used. Specific examples of triols includeglycerin, trimethylol propane, and hexanetriol. Specific examples oftetraols include pentaerythritol and sorbitol.

Examples of high-molecular-weight polyols include polyether polyols suchas polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), andpolytetramethylene ether glycol (PTMG); condensed polyester polyols suchas polyethylene adipate (PEA), polybutylene adipate (PBA), andpolyhexamethylene adipate (PHMA); lactone polyester polyols such aspoly-ε-caprolactone (PCL); polycarbonate polyols such aspolyhexamethylene carbonate; and acrylic polyols. Two or more polyolsmay be used in combination. In light of feel at impact of the golf ball2, the high-molecular-weight polyol has a number average molecularweight of preferably not less than 400 and more preferably not less than1000. The number average molecular weight is preferably not greater than10000.

Examples of polyisocyanates, as a material for the urethane bond,include aromatic diisocyanates, alicyclic diisocyanates, and aliphaticdiisocyanates. Two or more types of diisocyanates may be used incombination.

Examples of aromatic diisocyanates include 2,4-toluene diisocyanate,2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI),1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate(TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate(TMXDI), and paraphenylene diisocyanate (PPDI). One example of aliphaticdiisocyanates is hexamethylene diisocyanate (HDI). Examples of alicyclicdiisocyanates include 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI),1,3-bis(isocyanatemethyl)cyclohexane (H₆XDI), isophorone diisocyanate(IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI).4,4′-dicyclohexylmethane diisocyanate is preferable.

Specific examples of the thermoplastic polyurethane include trade names“Elastollan NY80A”, “Elastollan NY82A”, “Elastollan NY84A”, “ElastollanNY85A”, “Elastollan NY88A”, “Elastollan NY90A”, “Elastollan NY95A”,“Elastollan NY97A”, “Elastollan NY585”, and “Elastollan KP016N”,manufactured by BASF Japan Ltd.; and trade names “RESAMINE P4585LS” and“RESAMINE PS62490”, manufactured by Dainichiseika Color & Chemicals Mfg.Co., Ltd.

The resin composition of the cover 8 may include a coloring agent, afiller, a dispersant, an antioxidant, an ultraviolet absorber, a lightstabilizer, a fluorescent material, a fluorescent brightener, and thelike in an adequate amount. When the hue of the golf ball 2 is white, atypical coloring agent is titanium dioxide.

In light of durability of the cover 8, the cover 8 has a Shore Dhardness He of preferably not less than 15, more preferably not lessthan 18, and particularly preferably not less than 20. In light ofcontrollability upon an approach shot, the hardness He is preferably notgreater than 40, more preferably not greater than 36, and particularlypreferably not greater than 33.

The hardness He of the cover 8 is measured according to the standards of“ASTM-D 2240-68”. The hardness He is measured with a Shore D typehardness scale mounted to an automated hardness meter (trade name “digitest II” manufactured by Heinrich Bareiss Prüfgerätebau GmbH). For themeasurement, a sheet that is formed by hot press, is formed from thesame material as that of the cover 8, and has a thickness of about 2 mmis used. Prior to the measurement, a sheet is kept at 23° C. for twoweeks. At the measurement, three sheets are stacked.

In light of controllability upon an approach shot, the cover 8 has athickness Tc of preferably not less than 0.1 mm, more preferably notless than 0.3 mm, and particularly preferably not less than 0.4 mm. Inlight of spin suppression upon a shot with a driver, the thickness Tc ispreferably not greater than 2.0 mm, more preferably not greater than 1.5mm, and particularly preferably not greater than 1.0 mm. The thicknessTc is measured at a position immediately below the land 12.

For forming the cover 8, known methods such as injection molding,compression molding, and the like can be used. When forming the cover 8,the dimples 10 are formed by pimples formed on the cavity face of amold.

The golf ball 2 may include a reinforcing layer between the mid layer 6and the cover 8. The reinforcing layer firmly adheres to the mid layer 6and also to the cover 8. The reinforcing layer suppresses separation ofthe mid layer 6 from the cover 8. The reinforcing layer is formed from aresin composition. Examples of a preferable base polymer of thereinforcing layer include two-component curing type epoxy resins andtwo-component curing type urethane resins.

The golf ball 2 preferably has an amount of compressive deformation Sbof not less than 2.0 mm and not greater than 3.8 mm. The golf ball 2having an amount of compressive deformation Sb of not less than 2.0 mmhas excellent controllability upon an approach shot. From thisviewpoint, the amount of compressive deformation Sb is preferably notless than 2.2 mm and particularly preferably not less than 2.3 mm. Thegolf ball 2 having an amount of compressive deformation Sb of notgreater than 3.8 mm has excellent flight performance upon a shot with adriver. From this viewpoint, the amount of compressive deformation Sb ismore preferably not greater than 3.5 mm and particularly preferably notgreater than 3.2 mm.

For measurement of the amount of compressive deformation Sb, a YAMADAtype compression tester is used. In the tester, the golf ball 2 isplaced on a hard plate made of metal. Next, a cylinder made of metalgradually descends toward the golf ball 2. The golf ball 2, squeezedbetween the bottom face of the cylinder and the hard plate, becomesdeformed. A migration distance of the cylinder, starting from the statein which an initial load of 98 N is applied to the golf ball 2 up to thestate in which a final load of 1274 N is applied thereto, is measured. Amoving speed of the cylinder until the initial load is applied is 0.83mm/s. A moving speed of the cylinder after the initial load is applieduntil the final load is applied is 1.67 mm/s.

In the golf ball 2, the Shore C hardness Hmc of the mid layer 6 isgreater than the Shore C hardness Hs at the surface of the core 4. Inthe golf ball 2 in which the hardness Hmc is greater than the hardnessHs, the sphere consisting of the core 4 and the mid layer 6 has anouter-hard/inner-soft structure. When the golf ball 2 including thesphere is hit with a golf club, spin is suppressed. When the golf ball 2including the sphere is hit with a golf club, a high launch angle isobtained. The sphere has excellent flight performance.

In light of flight performance, the difference (Hmc−Hs) between thehardness Hmc and the hardness Hs is preferably not less than 5, morepreferably not less than 8, and particularly preferably not less than10. In light of resilience performance, the difference (Hmc−Hs) ispreferably not greater than 30, more preferably not greater than 25, andparticularly preferably not greater than 20.

The Shore D hardness He of the cover 8 is less than the Shore D hardnessHm of the mid layer 6. When the golf ball 2 in which the hardness He isless than the hardness Hm is hit with a short iron, a high spin rate isobtained. The golf ball 2 has excellent controllability upon an approachshot.

In light of controllability, the difference (Hm−Hc) between the hardnessHm and the hardness He is preferably not less than 20, more preferablynot less than 25, and particularly preferably not less than 30. In lightof resilience performance, the difference (Hm−Hc) is preferably notgreater than 50, more preferably not greater than 45, and particularlypreferably not greater than 42.

In the golf ball 2, a value V1 calculated by the following mathematicalformula exceeds 90.

V1=(DH*Hm)/(Hc*Tc)

In other words, the golf ball 2 satisfies the following mathematicalformula (i).

(DH*Hm)/(Hc*Tc)>90  (i)

According to the finding by the present inventor, the value V1correlates with the spin rate upon a shot with a driver. With the golfball 2 that satisfies the mathematical formula (i), the spin upon a shotwith a driver is suppressed. The golf ball 2 has excellent flightperformance upon a short with a driver. From this viewpoint, the valueV1 is more preferably not less than 100 and particularly preferably notless than 105. In light of feel at impact, the value V1 is preferablynot greater than 140.

In the golf ball 2, a value V2 calculated by the following mathematicalformula exceeds 0.60.

V2=((Sb*Tc)/(Hc*Hm*Tm))*1000)

In other words, the golf ball 2 satisfies the following mathematicalformula (ii).

((Sb*Tc)/(Hc*Hm*Tm))*1000>0.60  (ii)

According to the finding by the present inventor, the value V2correlates with the feel at impact upon a shot with a driver. With thegolf ball 2 that satisfies the mathematical formula (ii), soft feel atimpact is obtained upon a shot with a driver. From this viewpoint, thevalue V2 is more preferably not less than 0.70 and particularlypreferably not less than 0.80. In light of flight performance, the valueV2 is preferably not greater than 1.20.

In the golf ball 2 that includes the cover 8 having a low hardness Heand a small thickness Tc, the mathematical formulas (i) and (ii) can besatisfied.

As shown in FIGS. 2 and 3, the contour of each dimple 10 is circular.The golf ball 2 has dimples A each having a diameter of 4.40 mm; dimplesB each having a diameter of 4.30 mm; dimples C each having a diameter of4.15 mm; dimples D each having a diameter of 3.90 mm; and dimples E eachhaving a diameter of 3.00 mm. The number of types of the dimples 10 isfive. The golf ball 2 may have non-circular dimples instead of thecircular dimples 10 or together with the circular dimples 10.

The number of the dimples A is 60; the number of the dimples B is 158;the number of the dimples C is 72; the number of the dimples D is 36;and the number of the dimples E is 12. The total number of the dimples10 is 338. A dimple pattern is formed by these dimples 10 and the land12.

FIG. 4 shows a cross section of the golf ball 2 along a plane passingthrough the central point of the dimple 10 and the central point of thegolf ball 2. In FIG. 4, the top-to-bottom direction is the depthdirection of the dimple 10. In FIG. 4, a chain double-dashed line 14indicates a phantom sphere 14. The surface of the phantom sphere 14 isthe surface of the golf ball 2 when it is postulated that no dimple 10exists. The diameter of the phantom sphere 14 is equal to the diameterof the golf ball 2. The dimple 10 is recessed from the surface of thephantom sphere 14. The land 12 coincides with the surface of the phantomsphere 14. In the present embodiment, the cross-sectional shape of eachdimple 10 is substantially a circular arc. The curvature radius of thiscircular arc is shown by reference character CR in FIG. 4.

In FIG. 4, an arrow Dm indicates the diameter of the dimple 10. Thediameter Dm is the distance between two tangent points Ed appearing on atangent line Tg that is drawn tangent to the far opposite ends of thedimple 10. Each tangent point Ed is also the edge of the dimple 10. Theedge Ed defines the contour of the dimple 10.

The diameter Dm of each dimple 10 is preferably not less than 2.0 mm andnot greater than 6.0 mm. The dimple 10 having a diameter Dm of not lessthan 2.0 mm contributes to turbulization. The golf ball 2 having thedimples 10 has excellent flight performance. From this viewpoint, thediameter Dm is more preferably not less than 2.5 mm and particularlypreferably not less than 2.8 mm. The dimple 10 having a diameter Dm ofnot greater than 6.0 mm does not impair a fundamental feature of thegolf ball 2 being substantially a sphere. From this viewpoint, thediameter Dm is more preferably not greater than 5.5 mm and particularlypreferably not greater than 5.0 mm.

In the case of a non-circular dimple, a circular dimple 10 having thesame area as that of the non-circular dimple is assumed. The diameter ofthe assumed circular dimple 10 can be regarded as the diameter of thenon-circular dimple.

In FIG. 4, a double ended arrow Dp1 indicates a first depth of thedimple 10. The first depth Dp1 is the distance between the deepest partof the dimple 10 and the surface of the phantom sphere 14. In FIG. 4, adouble ended arrow Dp2 indicates a second depth of the dimple 10. Thesecond depth Dp2 is the distance between the deepest part of the dimple10 and the tangent line Tg.

In light of suppression of rising of the golf ball 2 during flight, thefirst depth Dp1 of each dimple 10 is preferably not less than 0.10 mm,more preferably not less than 0.13 mm, and particularly preferably notless than 0.15 mm. In light of suppression of dropping of the golf ball2 during flight, the first depth Dp1 is preferably not greater than 0.65mm, more preferably not greater than 0.60 mm, and particularlypreferably not greater than 0.55 mm.

The area S of the dimple 10 is the area of a region surrounded by thecontour line of the dimple 10 when the central point of the golf ball 2is viewed at infinity. In the case of a circular dimple 10, the area Sis calculated by the following mathematical formula.

S=(Dm/2)²*π

In the golf ball 2 shown in FIGS. 2 and 3, the area of each dimple A is15.20 mm²; the area of each dimple B is 14.52 mm²; the area of eachdimple C is 13.53 mm²; the area of each dimple D is 11.95 mm²; and thearea of each dimple E is 7.07 mm².

In the present invention, the ratio of the sum of the areas S of all thedimples 10 relative to the surface area of the phantom sphere 14 isreferred to as an occupation ratio. From the viewpoint of achievingsufficient turbulization, the occupation ratio is preferably not lessthan 78%, more preferably not less than 80%, and particularly preferablynot less than 82%. The occupation ratio is preferably not greater than95%. In the golf ball 2 shown in FIGS. 2 and 3, the total area of thedimples 10 is 4695.4 mm². The surface area of the phantom sphere 14 ofthe golf ball 2 is 5728 mm², so that the occupation ratio is 82.0%.

From the viewpoint of achieving a sufficient occupation ratio, the totalnumber N of the dimples 10 is preferably not less than 250, morepreferably not less than 280, and particularly preferably not less than300. From the viewpoint that each dimple 10 can contribute toturbulization, the total number N of the dimples 10 is preferably notgreater than 450, more preferably not greater than 400, and particularlypreferably not greater than 380.

In the present invention, the “volume V of the dimple” means the volumeof a portion surrounded by the surface of the phantom sphere 14 and thesurface of the dimple 10. The total volume TV of the dimples 10 ispreferably not less than 450 mm³ and not greater than 750 mm³. With thegolf ball 2 having a total volume TV of not less than 450 mm³, rising ofthe golf ball 2 during flight is suppressed. From this viewpoint, thetotal volume TV is more preferably not less than 480 mm³ andparticularly preferably not less than 500 mm³. With the golf ball 2having a total volume TV of not greater than 750 mm³, dropping of thegolf ball 2 during flight is suppressed. From this viewpoint, the totalvolume TV is more preferably not greater than 730 mm³ and particularlypreferably not greater than 710 mm³.

The golf ball 2 according to the present invention has an excellentaerodynamic characteristic. In an evaluation method for the aerodynamiccharacteristic, the following steps (a) to (h) are executed:

(a) assuming a great circle that is present on the surface of thephantom sphere 14 and is orthogonal to an axis Ax;

(b) assuming two small circles that are present on the surface of thephantom sphere 14, that are orthogonal to the axis Ax, and of which theabsolute values of central angles with the great circle are each 30°;

(c) defining a region, of the surface of the golf ball 2, which isobtained by dividing the surface of the golf ball 2 at these smallcircles and which is sandwiched between these small circles;

(d) determining 30240 points, on the region, arranged at intervals of acentral angle of 3° in a direction of the axis Ax and at intervals of acentral angle of 0.25° in a direction of rotation about the axis Ax;

(e) calculating the length L1 of a perpendicular line that extends fromeach point to the axis Ax;

(f) calculating a total length L2 by summing 21 lengths L1 calculated onthe basis of 21 perpendicular lines arranged in the direction of theaxis Ax; (g) obtaining a transformed data constellation by performingFourier transformation on a data constellation of 1440 total lengths L2calculated along the direction of rotation about the axis Ax; and

(h) calculating the peak value and the order of the maximum peak of thetransformed data constellation. The following will describe each step indetail.

FIG. 5 is a schematic diagram for explaining this evaluation method.FIG. 5 shows the phantom sphere 14 of the golf ball 2. In FIG. 5,reference character NP represents a north pole. The north pole NPcorresponds to the top of a cavity face formed by an upper mold half formolding the golf ball 2. Reference character SP represents a south pole.The south pole SP corresponds to the deepest part of a cavity faceformed by a lower mold half for molding the golf ball 2. Referencecharacter Eq represents an equator. The phantom sphere 14 can be dividedinto a northern hemisphere NH and a southern hemisphere SH by theequator Eq.

The latitude of the north pole NP is 90° (degrees). The latitude θ ofthe equator Eq is zero. The latitude of the south pole SP is −90°. Thecounterclockwise direction when the phantom sphere 14 is seen from thenorth pole NP is a positive direction of longitude ϕ. The minimum valueof ϕ is zero. The maximum value of ϕ is 360°. The spherical polarcoordinates of a point present on the surface of the phantom sphere 14are represented by (θ, ϕ). In FIG. 5, a point (0, 0) is located in thefront.

In FIG. 5, reference character Loa represents a first longitude line.The longitude ϕ of the first longitude line Loa is 0° and also 360°. Thephantom sphere 14 has numerous longitude lines. A longitude line thatcontains the maximum number of dimples 10 that centrally intersect thelongitude line is defined as the first longitude line Loa. At a dimple10 that centrally intersects a longitude line, the longitude line passesthrough the area center of gravity of the dimple 10.

In this evaluation method, a first axis Ax1 is assumed. The first axisAx1 passes through a point Pn1 and a point Ps1. The point Pn1 and thepoint Ps1 are present on the surface of the phantom sphere 14. The pointPn1 is present on the northern hemisphere NH. The coordinates of thepoint Pn1 are (75, 270). The point Ps1 is present on the southernhemisphere SH. The coordinates of the point Ps1 are (−75, 90). The firstaxis Ax1 is tilted relative to the earth axis. The angle of the tilt is15°. The earth axis is a line passing through the north pole NP and thesouth pole SP.

In this evaluation method, a first great circle GC1 that is present onthe surface of the phantom sphere 14 of the golf ball 2 is assumed. Thefirst axis Ax1 is orthogonal to the first great circle GC1. In otherwords, the first axis Ax1 is orthogonal to the plane including the firstgreat circle GC1. In FIG. 5, the first great circle GC1 is tiltedrelative to the equator Eq. The angle of the tilt is 15°. The greatcircle is a circle that is present on the surface of the phantom sphere14 and has a diameter equal to the diameter of the phantom sphere 14.

The golf ball 2 rotates about the first axis Ax1. During this rotation,the circumferential speed of the first great circle GC1 is high.Therefore, the surface roughness of the golf ball 2 at and near thefirst great circle GC1 greatly influences the flight performance of thegolf ball 2.

In this evaluation method, two small circles C1 and C2 that are presenton the surface of the phantom sphere 14 and are orthogonal to the firstaxis Ax1 are assumed. FIG. 6 shows these small circles C1 and C2. Eachsmall circle is parallel to the first great circle GC1.

FIG. 7 schematically shows a partial cross section of the golf ball 2 inFIG. 6. FIG. 7 shows a cross-section passing through the center O of thegolf ball 2. The right-left direction in FIG. 7 is the direction of thefirst axis Ax1. As shown in FIG. 7, the absolute value of the centralangle between the small circle C1 and the first great circle GC1 is 30°.Although not shown, the absolute value of the central angle between thesmall circle C2 and the first great circle GC1 is also 30°. The golfball 2 is divided at the small circles C1 and C2, and of the surface ofthe golf ball 2, a region sandwiched between the small circles C1 and C2is defined. Since the circumferential speed of the first great circleGC1 is high, the dimples 10 present in this region greatly influence theaerodynamic characteristic of the golf ball 2.

In FIG. 7, a point P(α) is the point that is located on the surface ofthe golf ball 2 and of which the central angle with the first greatcircle GC1 is α° (degrees). A point F(α) is the foot of a perpendicularline Pe(α) that extends downward from the point P(α) to the first axisAx1. An arrow L1(α) represents the length of the perpendicular linePe(α). In other words, the length L1(α) is the distance between thepoint P(α) and the first axis Ax1. For one cross section, the lengthsL1(α) are calculated at 21 points P(α). Specifically, the lengths L1(α)are calculated at angles α of −30θ, −27°, −24°, −21°, −18°, −15°, −12°,−9°, −6°, −3°, 0°, 3°, 6°, 9°, 12°, 15°, 18°, 21°, 24°, 27°, and 30°.The 21 lengths L1(α) are summed, thereby obtaining a total length L2(mm). The total length L2 is a parameter dependent on the surface shapein the cross section shown in FIG. 7.

FIG. 8 shows a partial cross section of the golf ball 2. In FIG. 8, adirection perpendicular to the surface of the sheet is the direction ofthe first axis Ax1. In FIG. 8, reference character β represents arotation angle of the golf ball 2. In a range of equal to or greaterthan 0° and less than 360°, the rotation angles β are set at an intervalof an angle of 0.25°. At each rotation angle, the total length L2 iscalculated. As a result, 1440 total lengths L2 are obtained along therotation direction. These total lengths L2 are a data constellationcalculated through one rotation of the golf ball 2. This dataconstellation is calculated on the basis of 30240 lengths L1.

FIG. 9 shows a graph plotting the data constellation, for the first axisAx1, of the golf ball 2 shown in FIGS. 2 and 3. In this graph, thehorizontal axis represents the rotation angle β, and the vertical axisrepresents the total length L2. Fourier transformation is performed onthe data constellation. By the Fourier transformation, a frequencyspectrum is obtained. In other words, by the Fourier transformation, acoefficient of a Fourier series represented by the following formula isobtained.

$F_{k} = {\sum\limits_{n = 0}^{N - 1}\; ( {{a_{n}\cos \; 2\; \pi \; \frac{nk}{N}} + {b_{n}\sin \; 2\; \pi \; \frac{nk}{N}}} )}$

The above mathematical formula is a combination of two trigonometricfunctions having different periods. In the above mathematical formula,a_(n) and b_(n) are Fourier coefficients. The magnitude of eachcomponent to be combined is determined depending on these Fouriercoefficients. Each coefficient is represented by the followingmathematical formula.

$a_{n} = {{\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}{F_{k}\; \cos \; 2\; \pi \; \frac{nk}{N}\mspace{45mu} b_{n}}}} = {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{F_{k}\; \sin \; 2\; \pi \; \frac{nk}{N}}}}}$

In the above mathematical formulas, N is the total number of pieces ofdata of the data constellation, and F_(k) is the kth value in the dataconstellation. The spectrum is represented by the following mathematicalformula.

P _(n)=√{square root over (a _(n) ² +b _(n) ²)}

By the Fourier transformation, a transformed data constellation isobtained. FIG. 10 shows a graph plotting the transformed dataconstellation. In this graph, the horizontal axis represents an order,and the vertical axis represents an amplitude. From this graph, themaximum peak is determined. Furthermore, the peak value Pd1 of themaximum peak and the order Fd1 of the maximum peak are determined. Thepeak value Pd1 and the order Fd1 are numeric values representing theaerodynamic characteristic during rotation about the first axis Ax1. Inthe present embodiment, the peak value Pd1 is 270.2 mm, and the orderFd1 is 33.

FIG. 11 also shows the phantom sphere 14 of the golf ball 2. FIG. 11shows the equator Eq and the longitude line Loa having a longitude ϕ ofzero. In FIG. 11, the point (0, 0) is located in the front. In FIG. 11,reference character Ax2 represents a second axis. The second axis Ax2passes through a point Pn2 and a point Ps2. The point Pn2 and the pointPs2 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn2 are (60, 270). The coordinates of the point Ps2 are(−60, 90). The second axis Ax2 is tilted relative to the earth axis. Theangle of the tilt is 30°.

FIG. 11 shows a second great circle GC2 that is present on the surfaceof the phantom sphere 14 of the golf ball 2 and to which the second axisAx2 is orthogonal. The second great circle GC2 is tilted relative to theequator Eq. The angle of the tilt is 30°.

For rotation about the second axis Ax2, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the second axis Ax2, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the second great circle GC2 is 30°. Theabsolute value of the central angle between the small circle C2 and thesecond great circle GC2 is also 30°. In the region, of the surface ofthe golf ball 2, sandwiched between these small circles, 1440 totallengths L2 are calculated. In other words, a data constellation for thesecond axis Ax2 is calculated. Fourier transformation is performed onthis data constellation, thereby obtaining a transformed dataconstellation. From a graph plotting the transformed data constellation,the peak value Pd2 of the maximum peak and the order Fd2 of the maximumpeak are determined. The peak value Pd2 and the order Fd2 are numericvalues representing the aerodynamic characteristic during rotation aboutthe second axis Ax2. In the present embodiment, the peak value Pd2 is177.9 mm, and the order Fd2 is 37.

FIG. 12 also shows the phantom sphere 14 of the golf ball 2. FIG. 12shows the equator Eq and the longitude line Loa having a longitude 1 ofzero. In FIG. 12, the point (0, 0) is located in the front. In FIG. 12,reference character Ax3 represents a third axis. The third axis Ax3passes through a point Pn3 and a point Ps3. The point Pn3 and the pointPs3 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn3 are (45, 270). The coordinates of the point Ps3 are(−45, 90). The third axis Ax3 is tilted relative to the earth axis. Theangle of the tilt is 45°.

FIG. 12 shows a third great circle GC3 that is present on the surface ofthe phantom sphere 14 of the golf ball 2 and to which the third axis Ax3is orthogonal. The third great circle GC3 is tilted relative to theequator Eq. The angle of the tilt is 45°.

For rotation about the third axis Ax3, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the third axis Ax3, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the third great circle GC3 is 30°. Theabsolute value of the central angle between the small circle C2 and thethird great circle GC3 is also 30°. In the region, of the surface of thegolf ball 2, sandwiched between these small circles, 1440 total lengthsL2 are calculated. In other words, a data constellation for the thirdaxis Ax3 is calculated. Fourier transformation is performed on this dataconstellation, thereby obtaining a transformed data constellation. Froma graph plotting the transformed data constellation, the peak value Pd3of the maximum peak and the order Fd3 of the maximum peak aredetermined. The peak value Pd3 and the order Fd3 are numeric valuesrepresenting the aerodynamic characteristic during rotation about thethird axis Ax3. In the present embodiment, the peak value Pd3 is 150.2mm, and the order Fd3 is 37.

FIG. 13 also shows the phantom sphere 14 of the golf ball 2. FIG. 13shows the equator Eq and the longitude line Loa having a longitude ϕ ofzero. In FIG. 13, the point (0, 0) is located in the front. In FIG. 13,reference character Ax4 represents a fourth axis. The fourth axis Ax4passes through a point Pn4 and a point Ps4. The point Pn4 and the pointPs4 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn4 are (30, 270). The coordinates of the point Ps4 are(−30, 90). The fourth axis Ax4 is tilted relative to the earth axis. Theangle of the tilt is 60°.

FIG. 13 shows a fourth great circle GC4 that is present on the surfaceof the phantom sphere 14 of the golf ball 2 and to which the fourth axisAx4 is orthogonal. The fourth great circle GC4 is tilted relative to theequator Eq. The angle of the tilt is 60°.

For rotation about the fourth axis Ax4, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the fourth axis Ax4, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the fourth great circle GC4 is 30°. Theabsolute value of the central angle between the small circle C2 and thefourth great circle GC4 is also 30°. In the region, of the surface ofthe golf ball 2, sandwiched between these small circles, 1440 totallengths L2 are calculated. In other words, a data constellation for thefourth axis Ax4 is calculated. Fourier transformation is performed onthis data constellation, thereby obtaining a transformed dataconstellation. From a graph plotting the transformed data constellation,the peak value Pd4 of the maximum peak and the order Fd4 of the maximumpeak are determined. The peak value Pd4 and the order Fd4 are numericvalues representing the aerodynamic characteristic during rotation aboutthe fourth axis Ax4. In the present embodiment, the peak value Pd4 is316.4 mm, and the order Fd4 is 34.

FIG. 14 also shows the phantom sphere 14 of the golf ball 2. FIG. 14shows the equator Eq and the longitude line Loa having a longitude ϕ ofzero. In FIG. 14, the point (0, 0) is located in the front. In FIG. 14,reference character Ax5 represents a fifth axis. The fifth axis Ax5passes through a point Pn5 and a point Ps5. The point Pn5 and the pointPs5 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn5 are (15, 270). The coordinates of the point Ps5 are(−15, 90). The fifth axis Ax5 is tilted relative to the earth axis. Theangle of the tilt is 75°.

FIG. 14 shows a fifth great circle GC5 that is present on the surface ofthe phantom sphere 14 of the golf ball 2 and to which the fifth axis Ax5is orthogonal. The fifth great circle GC5 is tilted relative to theequator Eq. The angle of the tilt is 75°.

For rotation about the fifth axis Ax5, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the fifth axis Ax5, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the fifth great circle GC5 is 30°. Theabsolute value of the central angle between the small circle C2 and thefifth great circle GC5 is also 30°. In the region, of the surface of thegolf ball 2, sandwiched between these small circles, 1440 total lengthsL2 are calculated. In other words, a data constellation for the fifthaxis Ax5 is calculated. Fourier transformation is performed on this dataconstellation, thereby obtaining a transformed data constellation. Froma graph plotting the transformed data constellation, the peak value Pd5of the maximum peak and the order Fd5 of the maximum peak aredetermined. The peak value Pd5 and the order Fd5 are numeric valuesrepresenting the aerodynamic characteristic during rotation about thefifth axis Ax5. In the present embodiment, the peak value Pd5 is 190.0mm, and the order Fd5 is 27.

FIG. 15 also shows the phantom sphere 14 of the golf ball 2. FIG. 15shows the equator Eq and a longitude line Lob having a longitude ϕ of90°. In FIG. 15, a point (0, 90) is located in the front. In FIG. 15,reference character Ax6 represents a sixth axis. The sixth axis Ax6passes through a point Pn6 and a point Ps6. The point Pn6 and the pointPs6 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn6 are (75, 0). The coordinates of the point Ps6 are (−75,180). The sixth axis Ax6 is tilted relative to the earth axis. The angleof the tilt is 150.

FIG. 15 shows a sixth great circle GC6 that is present on the surface ofthe phantom sphere 14 of the golf ball 2 and to which the sixth axis Ax6is orthogonal. The sixth great circle GC6 is tilted relative to theequator Eq. The angle of the tilt is 15°.

For rotation about the sixth axis Ax6, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the sixth axis Ax6, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the sixth great circle GC6 is 30°. Theabsolute value of the central angle between the small circle C2 and thesixth great circle GC6 is also 30°. In the region, of the surface of thegolf ball 2, sandwiched between these small circles, 1440 total lengthsL2 are calculated. In other words, a data constellation for the sixthaxis Ax6 is calculated. Fourier transformation is performed on this dataconstellation, thereby obtaining a transformed data constellation. Froma graph plotting the transformed data constellation, the peak value Pd6of the maximum peak and the order Fd6 of the maximum peak aredetermined. The peak value Pd6 and the order Fd6 are numeric valuesrepresenting the aerodynamic characteristic during rotation about thesixth axis Ax6. In the present embodiment, the peak value Pd6 is 270.2mm, and the order Fd6 is 33.

FIG. 16 also shows the phantom sphere 14 of the golf ball 2. FIG. 16shows the equator Eq and the longitude line Lob having a longitude ϕ of90°. In FIG. 16, the point (0, 90) is located in the front. In FIG. 16,reference character Ax7 represents a seventh axis. The seventh axis Ax7passes through a point Pn7 and a point Ps7. The point Pn7 and the pointPs7 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn7 are (60, 0). The coordinates of the point Ps7 are (−60,180). The seventh axis Ax7 is tilted relative to the earth axis. Theangle of the tilt is 30°.

FIG. 16 shows a seventh great circle GC7 that is present on the surfaceof the phantom sphere 14 of the golf ball 2 and to which the seventhaxis Ax7 is orthogonal. The seventh great circle GC7 is tilted relativeto the equator Eq. The angle of the tilt is 30°.

For rotation about the seventh axis Ax7, an aerodynamic characteristicis evaluated by the same method as that for rotation about the firstaxis Ax1. Specifically, for rotation about the seventh axis Ax7, twosmall circles C1 and C2 are assumed. The absolute value of the centralangle between the small circle C1 and the seventh great circle GC7 is30°. The absolute value of the central angle between the small circle C2and the seventh great circle GC7 is also 30°. In the region, of thesurface of the golf ball 2, sandwiched between these small circles, 1440total lengths L2 are calculated. In other words, a data constellationfor the seventh axis Ax7 is calculated. Fourier transformation isperformed on this data constellation, thereby obtaining a transformeddata constellation. From a graph plotting the transformed dataconstellation, the peak value Pd7 of the maximum peak and the order Fd7of the maximum peak are determined. The peak value Pd7 and the order Fd7are numeric values representing the aerodynamic characteristic duringrotation about the seventh axis Ax7. In the present embodiment, the peakvalue Pd7 is 177.9 mm, and the order Fd7 is 37.

FIG. 17 also shows the phantom sphere 14 of the golf ball 2. FIG. 17shows the equator Eq and the longitude line Lob having a longitude of90°. In FIG. 17, the point (0, 90) is located in the front. In FIG. 17,reference character Ax8 represents an eighth axis. The eighth axis Ax8passes through a point Pn8 and a point Ps8. The point Pn8 and the pointPs8 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn8 are (45, 0). The coordinates of the point Ps8 are (−45,180). The eighth axis Ax8 is tilted relative to the earth axis. Theangle of the tilt is 45°.

FIG. 17 shows an eighth great circle GC8 that is present on the surfaceof the phantom sphere 14 of the golf ball 2 and to which the eighth axisAx8 is orthogonal. The eighth great circle GC8 is tilted relative to theequator Eq. The angle of the tilt is 45°.

For rotation about the eighth axis Ax8, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the eighth axis Ax8, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the eighth great circle GC8 is 30°. Theabsolute value of the central angle between the small circle C2 and theeighth great circle GC8 is also 30°. In the region, of the surface ofthe golf ball 2, sandwiched between these small circles, 1440 totallengths L2 are calculated. In other words, a data constellation for theeighth axis Ax8 is calculated. Fourier transformation is performed onthis data constellation, thereby obtaining a transformed dataconstellation. From a graph plotting the transformed data constellation,the peak value Pd8 of the maximum peak and the order Fd8 of the maximumpeak are determined. The peak value Pd8 and the order Fd8 are numericvalues representing the aerodynamic characteristic during rotation aboutthe eighth axis Ax8. In the present embodiment, the peak value Pd8 is150.2 mm, and the order Fd8 is 37.

FIG. 18 also shows the phantom sphere 14 of the golf ball 2. FIG. 18shows the equator Eq and the longitude line Lob having a longitude ϕ of90°. In FIG. 18, the point (0, 90) is located in the front. In FIG. 18,reference character Ax9 represents a ninth axis. The ninth axis Ax9passes through a point Pn9 and a point Ps9. The point Pn9 and the pointPs9 are present on the surface of the phantom sphere 14. The coordinatesof the point Pn9 are (30, 0). The coordinates of the point Ps9 are (−30,180). The ninth axis Ax9 is tilted relative to the earth axis. The angleof the tilt is 60°.

FIG. 18 shows a ninth great circle GC9 that is present on the surface ofthe phantom sphere 14 of the golf ball 2 and to which the ninth axis Ax9is orthogonal. The ninth great circle GC9 is tilted relative to theequator Eq. The angle of the tilt is 60°.

For rotation about the ninth axis Ax9, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the ninth axis Ax9, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the ninth great circle GC9 is 30°. Theabsolute value of the central angle between the small circle C2 and theninth great circle GC9 is also 30°. In the region, of the surface of thegolf ball 2, sandwiched between these small circles, 1440 total lengthsL2 are calculated. In other words, a data constellation for the ninthaxis Ax9 is calculated. Fourier transformation is performed on this dataconstellation, thereby obtaining a transformed data constellation. Froma graph plotting the transformed data constellation, the peak value Pd9of the maximum peak and the order Fd9 of the maximum peak aredetermined. The peak value Pd9 and the order Fd9 are numeric valuesrepresenting the aerodynamic characteristic during rotation about theninth axis Ax9. In the present embodiment, the peak value Pd9 is 316.4mm, and the order Fd9 is 34.

FIG. 19 also shows the phantom sphere 14 of the golf ball 2. FIG. 19shows the equator Eq and the longitude line Lob having a longitude ϕ of90°. In FIG. 19, the point (0, 90) is located in the front. In FIG. 19,reference character Ax10 represents a tenth axis. The tenth axis Ax10passes through a point Pn10 and a point Ps10. The point Pn10 and thepoint Ps10 are present on the surface of the phantom sphere 14. Thecoordinates of the point Pn10 are (15, 0). The coordinates of the pointPs10 are (−15, 180). The tenth axis Ax10 is tilted relative to the earthaxis. The angle of the tilt is 75°.

FIG. 19 shows a tenth great circle GC10 that is present on the surfaceof the phantom sphere 14 of the golf ball 2 and to which the tenth axisAx10 is orthogonal. The tenth great circle GC10 is tilted relative tothe equator Eq. The angle of the tilt is 75°.

For rotation about the tenth axis Ax10, an aerodynamic characteristic isevaluated by the same method as that for rotation about the first axisAx1. Specifically, for rotation about the tenth axis Ax10, two smallcircles C1 and C2 are assumed. The absolute value of the central anglebetween the small circle C1 and the tenth great circle GC10 is 30°. Theabsolute value of the central angle between the small circle C2 and thetenth great circle GC10 is also 30°. In the region, of the surface ofthe golf ball 2, sandwiched between these small circles, 1440 totallengths L2 are calculated. In other words, a data constellation for thetenth axis Ax10 is calculated. Fourier transformation is performed onthis data constellation, thereby obtaining a transformed dataconstellation. From a graph plotting the transformed data constellation,the peak value Pd10 of the maximum peak and the order Fd10 of themaximum peak are determined. The peak value Pd10 and the order Fd10 arenumeric values representing the aerodynamic characteristic duringrotation about the tenth axis Ax10. In the present embodiment, the peakvalue Pd10 is 190.0 mm, and the order Fd10 is 27.

FIG. 20 also shows the phantom sphere 14 of the golf ball 2. FIG. 20shows the equator Eq and a longitude line Loc having a longitude of180°. In FIG. 20, a point (0, 180) is located in the front. In FIG. 20,reference character Ax11 represents an eleventh axis. The eleventh axisAx11 passes through a point Pn11 and a point Ps11. The point Pn11 andthe point Ps11 are present on the surface of the phantom sphere 14. Thecoordinates of the point Pn11 are (75, 90). The coordinates of the pointPs11 are (−75, 270). The eleventh axis Ax11 is tilted relative to theearth axis. The angle of the tilt is 15°.

FIG. 20 shows an eleventh great circle GC11 that is present on thesurface of the phantom sphere 14 of the golf ball 2 and to which theeleventh axis Ax11 is orthogonal. The eleventh great circle GC11 istilted relative to the equator Eq. The angle of the tilt is 15°.

For rotation about the eleventh axis Ax11, an aerodynamic characteristicis evaluated by the same method as that for rotation about the firstaxis Ax1. Specifically, for rotation about the eleventh axis Ax11, twosmall circles C1 and C2 are assumed. The absolute value of the centralangle between the small circle C1 and the eleventh great circle GC11 is30°. The absolute value of the central angle between the small circle C2and the eleventh great circle GC11 is also 30°. In the region, of thesurface of the golf ball 2, sandwiched between these small circles, 1440total lengths L2 are calculated. In other words, a data constellationfor the eleventh axis Ax11 is calculated. Fourier transformation isperformed on this data constellation, thereby obtaining a transformeddata constellation. From a graph plotting the transformed dataconstellation, the peak value Pd11 of the maximum peak and the orderFd11 of the maximum peak are determined. The peak value Pd11 and theorder Fd11 are numeric values representing the aerodynamiccharacteristic during rotation about the eleventh axis Ax11. In thepresent embodiment, the peak value Pd11 is 270.2 mm, and the order Fd11is 33.

FIG. 21 also shows the phantom sphere 14 of the golf ball 2. FIG. 21shows the equator Eq and the longitude line Loc having a longitude of180°. In FIG. 21, the point (0, 180) is located in the front. In FIG.21, reference character Ax12 represents a twelfth axis. The twelfth axisAx12 passes through a point Pn12 and a point Ps12. The point Pn12 andthe point Ps12 are present on the surface of the phantom sphere 14. Thecoordinates of the point Pn12 are (60, 90). The coordinates of the pointPs12 are (−60, 270). The twelfth axis Ax12 is tilted relative to theearth axis. The angle of the tilt is 30°.

FIG. 21 shows a twelfth great circle GC12 that is present on the surfaceof the phantom sphere 14 of the golf ball 2 and to which the twelfthaxis Ax12 is orthogonal. The twelfth great circle GC12 is tiltedrelative to the equator Eq. The angle of the tilt is 30°.

For rotation about the twelfth axis Ax12, an aerodynamic characteristicis evaluated by the same method as that for rotation about the firstaxis Ax1. Specifically, for rotation about the twelfth axis Ax12, twosmall circles C1 and C2 are assumed. The absolute value of the centralangle between the small circle C1 and the twelfth great circle GC12 is30°. The absolute value of the central angle between the small circle C2and the twelfth great circle GC12 is also 30°. In the region, of thesurface of the golf ball 2, sandwiched between these small circles, 1440total lengths L2 are calculated. In other words, a data constellationfor the twelfth axis Ax12 is calculated. Fourier transformation isperformed on this data constellation, thereby obtaining a transformeddata constellation. From a graph plotting the transformed dataconstellation, the peak value Pd12 of the maximum peak and the orderFd12 of the maximum peak are determined. The peak value Pd12 and theorder Fd12 are numeric values representing the aerodynamiccharacteristic during rotation about the twelfth axis Ax12. In thepresent embodiment, the peak value Pd12 is 177.9 mm, and the order Fd12is 37.

FIG. 22 also shows the phantom sphere 14 of the golf ball 2. FIG. 22shows the equator Eq and the longitude line Loc having a longitude p of180°. In FIG. 22, the point (0, 180) is located in the front. In FIG.22, reference character Ax13 represents a thirteenth axis. Thethirteenth axis Ax13 passes through a point Pn13 and a point Ps13. Thepoint Pn13 and the point Ps13 are present on the surface of the phantomsphere 14. The coordinates of the point Pn13 are (45, 90). Thecoordinates of the point Ps13 are (−45, 270). The thirteenth axis Ax13is tilted relative to the earth axis. The angle of the tilt is 45°.

FIG. 22 shows a thirteenth great circle GC13 that is present on thesurface of the phantom sphere 14 of the golf ball 2 and to which thethirteenth axis Ax13 is orthogonal. The thirteenth great circle GC13 istilted relative to the equator Eq. The angle of the tilt is 45°.

For rotation about the thirteenth axis Ax13, an aerodynamiccharacteristic is evaluated by the same method as that for rotationabout the first axis Ax1. Specifically, for rotation about thethirteenth axis Ax13, two small circles C1 and C2 are assumed. Theabsolute value of the central angle between the small circle C1 and thethirteenth great circle GC13 is 30°. The absolute value of the centralangle between the small circle C2 and the thirteenth great circle GC13is also 30°. In the region, of the surface of the golf ball 2,sandwiched between these small circles, 1440 total lengths L2 arecalculated. In other words, a data constellation for the thirteenth axisAx13 is calculated. Fourier transformation is performed on this dataconstellation, thereby obtaining a transformed data constellation. Froma graph plotting the transformed data constellation, the peak value Pd13of the maximum peak and the order Fd13 of the maximum peak aredetermined. The peak value Pd13 and the order Fd13 are numeric valuesrepresenting the aerodynamic characteristic during rotation about thethirteenth axis Ax13. In the present embodiment, the peak value Pd13 is150.2 mm, and the order Fd13 is 37.

FIG. 23 also shows the phantom sphere 14 of the golf ball 2. FIG. 23shows the equator Eq and the longitude line Loc having a longitude ϕ of180°. In FIG. 23, the point (0, 180) is located in the front. In FIG.23, reference character Ax14 represents a fourteenth axis. Thefourteenth axis Ax14 passes through a point Pn14 and a point Ps14. Thepoint Pn14 and the point Ps14 are present on the surface of the phantomsphere 14. The coordinates of the point Pn14 are (30, 90). Thecoordinates of the point Ps14 are (−30, 270). The fourteenth axis Ax14is tilted relative to the earth axis. The angle of the tilt is 60°.

FIG. 23 shows a fourteenth great circle GC14 that is present on thesurface of the phantom sphere 14 of the golf ball 2 and to which thefourteenth axis Ax14 is orthogonal. The fourteenth great circle GC14 istilted relative to the equator Eq. The angle of the tilt is 60°.

For rotation about the fourteenth axis Ax14, an aerodynamiccharacteristic is evaluated by the same method as that for rotationabout the first axis Ax1. Specifically, for rotation about thefourteenth axis Ax14, two small circles C1 and C2 are assumed. Theabsolute value of the central angle between the small circle C1 and thefourteenth great circle GC14 is 30°. The absolute value of the centralangle between the small circle C2 and the fourteenth great circle GC14is also 30°. In the region, of the surface of the golf ball 2,sandwiched between these small circles, 1440 total lengths L2 arecalculated. In other words, a data constellation for the fourteenth axisAx14 is calculated. Fourier transformation is performed on this dataconstellation, thereby obtaining a transformed data constellation. Froma graph plotting the transformed data constellation, the peak value Pd14of the maximum peak and the order Fd14 of the maximum peak aredetermined. The peak value Pd14 and the order Fd14 are numeric valuesrepresenting the aerodynamic characteristic during rotation about thefourteenth axis Ax14. In the present embodiment, the peak value Pd14 is316.4 mm, and the order Fd14 is 34.

FIG. 24 also shows the phantom sphere 14 of the golf ball 2. FIG. 24shows the equator Eq and the longitude line Loc having a longitude ϕ of180°. In FIG. 24, the point (0, 180) is located in the front. In FIG.24, reference character Ax15 represents a fifteenth axis. The fifteenthaxis Ax15 passes through a point Pn15 and a point Ps15. The point Pn15and the point Ps15 are present on the surface of the phantom sphere 14.The coordinates of the point Pn15 are (15, 90). The coordinates of thepoint Ps15 are (−15, 270). The fifteenth axis Ax15 is tilted relative tothe earth axis. The angle of the tilt is 75°.

FIG. 24 shows a fifteenth great circle GC15 that is present on thesurface of the phantom sphere 14 of the golf ball 2 and to which thefifteenth axis Ax15 is orthogonal. The fifteenth great circle GC15 istilted relative to the equator Eq. The angle of the tilt is 75°.

For rotation about the fifteenth axis Ax15, an aerodynamiccharacteristic is evaluated by the same method as that for rotationabout the first axis Ax1. Specifically, for rotation about the fifteenthaxis Ax15, two small circles C1 and C2 are assumed. The absolute valueof the central angle between the small circle C1 and the fifteenth greatcircle GC15 is 30°. The absolute value of the central angle between thesmall circle C2 and the fifteenth great circle GC15 is also 30°. In theregion, of the surface of the golf ball 2, sandwiched between thesesmall circles, 1440 total lengths L2 are calculated. In other words, adata constellation for the fifteenth axis Ax15 is calculated. Fouriertransformation is performed on this data constellation, therebyobtaining a transformed data constellation. From a graph plotting thetransformed data constellation, the peak value Pd15 of the maximum peakand the order Fd15 of the maximum peak are determined. The peak valuePd15 and the order Fd15 are numeric values representing the aerodynamiccharacteristic during rotation about the fifteenth axis Ax15. In thepresent embodiment, the peak value Pd15 is 190.0 mm, and the order Fd15is 27.

In this evaluation method, the steps (a) to (h) are executed for each of15 axes Ax that are

(1) the first axis Ax1 passing through the point Pn1 the coordinates ofwhich are (75, 270) and the point Ps1 the coordinates of which are (−75,90),

(2) the second axis Ax2 passing through the point Pn2 the coordinates ofwhich are (60, 270) and the point Ps2 the coordinates of which are (−60,90),

(3) the third axis Ax3 passing through the point Pn3 the coordinates ofwhich are (45, 270) and the point Ps3 the coordinates of which are (−45,90),

(4) the fourth axis Ax4 passing through the point Pn4 the coordinates ofwhich are (30, 270) and the point Ps4 the coordinates of which are (−30,90),

(5) the fifth axis Ax5 passing through the point Pn5 the coordinates ofwhich are (15, 270) and the point Ps5 the coordinates of which are (−15,90),

(6) the sixth axis Ax6 passing through the point Pn6 the coordinates ofwhich are (75, 0) and the point Ps6 the coordinates of which are (−75,180),

(7) the seventh axis Ax7 passing through the point Pn7 the coordinatesof which are (60, 0) and the point Ps7 the coordinates of which are(−60, 180),

(8) the eighth axis Ax8 passing through the point Pn8 the coordinates ofwhich are (45, 0) and the point Ps8 the coordinates of which are (−45,180),

(9) the ninth axis Ax9 passing through the point Pn9 the coordinates ofwhich are (30, 0) and the point Ps9 the coordinates of which are (−30,180),

(10) the tenth axis Ax10 passing through the point Pn10 the coordinatesof which are (15, 0) and the point Ps10 the coordinates of which are(−15, 180),

(11) the eleventh axis Ax11 passing through the point Pn11 thecoordinates of which are (75, 90) and the point Ps11 the coordinates ofwhich are (−75, 270),

(12) the twelfth axis Ax12 passing through the point Pn12 thecoordinates of which are (60, 90) and the point Ps12 the coordinates ofwhich are (−60, 270),

(13) the thirteenth axis Ax13 passing through the point Pn13 thecoordinates of which are (45, 90) and the point Ps13 the coordinates ofwhich are (−45, 270),

(14) the fourteenth axis Ax14 passing through the point Pn14 thecoordinates of which are (30, 90) and the point Ps14 the coordinates ofwhich are (−30, 270), and

(15) the fifteenth axis Ax15 passing through the point Pn15 thecoordinates of which are (15, 90) and the point Ps15 the coordinates ofwhich are (−15, 270). Accordingly, 15 peak values (Pd1 to Pd15) and 15orders (Fd1 to Fd15) are calculated.

The minimums among the 15 peak values (Pd1 to Pd15) are Pd3, Pd8, andPd13. The minimum value of the peak value Pd is 150.2 mm. According tothe findings by the present inventor, the minimum value is preferablynot less than 95 mm. In the golf ball 2 in which the minimum value isnot less than 95 mm, a sufficient dimple effect can be achieved evenduring rotation about any axis Ax. The golf ball 2 has a large flightdistance. From this viewpoint, the minimum value of the peak value Pd ismore preferably not less than 120 mm and particularly preferably notless than 140 mm.

The maximums among the 15 peak values (Pd1 to Pd15) are Pd4, Pd9, andPd14. The maximum value of the peak value Pd is 316.4 mm. According tothe findings by the present inventor, the maximum value is preferablynot greater than 500 mm. The golf ball 2 in which the maximum value isnot greater than 500 mm has an excellent aerodynamic characteristic. Thegolf ball 2 has a large flight distance. From this viewpoint, themaximum value of the peak value Pd is more preferably not greater than400 mm and particularly preferably not greater than 330 mm.

The average of the 15 peak values (Pd1 to Pd15) is preferably not lessthan 200 mm. The golf ball 2 in which the average is not less than 200mm has an excellent aerodynamic characteristic. The golf ball 2 has alarge flight distance. From this viewpoint, the average is morepreferably not less than 210 mm and particularly preferably not lessthan 220 mm. The average is preferably not greater than 300 mm andparticularly preferably not greater than 230 mm. In the presentembodiment, the average is 220.9 mm.

The minimums among the 15 orders (Fd1 to Fd15) are Fd5, Fd10, and Fd15.The minimum value of the order Fd is 27. According to the findings bythe present inventor, the minimum value is preferably not less than 27.The golf ball 2 in which the minimum value is not less than 27 has anexcellent aerodynamic characteristic. The golf ball 2 has a large flightdistance.

The maximums among the 15 orders (Fd1 to Fd15) are Fd2, Fd3, Fd7, Fd8,Fd12, and Fd13. The maximum value of the order Fd is 37. According tothe findings by the present inventor, the maximum value is preferablynot greater than 37. The golf ball 2 in which the maximum value is notgreater than 37 has an excellent aerodynamic characteristic. The golfball 2 has a large flight distance.

The average of the 15 orders (Fd1 to Fd15) is preferably not less than30 and not greater than 34. The golf ball 2 in which the average fallswithin this range has an excellent aerodynamic characteristic. The golfball 2 has a large flight distance. In the present embodiment, theaverage is 33.6.

In this method, the golf ball 2 is evaluated by the 15 peak values Pdand the 15 orders Fd based on the 15 axes Ax. By this method, theaerodynamic characteristic of the golf ball 2 can be objectivelyevaluated.

EXAMPLES Example 1

A rubber composition B was obtained by kneading 100 parts by weight of ahigh-cis polybutadiene (trade name “BR-730”, manufactured by JSRCorporation), 29.5 parts by weight of zinc diacrylate, 5 parts by weightof zinc oxide, an appropriate amount of barium sulfate, 0.9 parts byweight of dicumyl peroxide, 0.3 parts by weight of pentabromo diphenyldisulfide, 0.1 parts by weight of 2-naphthalenethiol, and 2.0 parts byweight of benzoic acid. The rubber composition B was placed into a moldincluding upper and lower mold halves each having a hemisphericalcavity, and heated at 150° C. for 20 minutes to obtain a core with adiameter of 39.7 mm.

A resin composition M1 was obtained by kneading 47 parts by weight of anionomer resin (the aforementioned “Himilan 1605”), 50 parts by weight ofanother ionomer resin (the aforementioned “Himilan AM7329”), 3 parts byweight of a styrene block-containing thermoplastic elastomer (theaforementioned “RABALON T3221C”), and 4 parts by weight of titaniumdioxide with a twin-screw kneading extruder. The core was covered withthe resin composition M1 by injection molding to form a mid layer with athickness of 1.0 mm.

A paint composition (trade name “POLIN 750LE”, manufactured by SHINTOPAINT CO., LTD.) including a two-component curing type epoxy resin as abase polymer was prepared. The base material liquid of this paintcomposition includes 30 parts by weight of a bisphenol A type epoxyresin and 70 parts by weight of a solvent. The curing agent liquid ofthis paint composition includes 40 parts by weight of a modifiedpolyamide amine, 55 parts by weight of a solvent, and 5 parts by weightof titanium dioxide. The weight ratio of the base material liquid to thecuring agent liquid is 1/1. This paint composition was applied to thesurface of the mid layer with a spray gun, and kept at 23° C. for 12hours to obtain a reinforcing layer with a thickness of 10 μm.

A resin composition C1 was obtained by kneading 100 parts by weight of athermoplastic polyurethane elastomer (the aforementioned “ElastollanNY80A”), 0.2 parts by weight of a light stabilizer (trade name “TINUVIN770”), and 4 parts by weight of titanium dioxide with a twin-screwkneading extruder. Half shells were obtained from the resin compositionC1 by compression molding. The sphere consisting of the core, the midlayer, and the reinforcing layer was covered with two of these halfshells. These half shells and the sphere were placed into a final moldthat includes upper and lower mold halves each having a hemisphericalcavity and having a large number of pimples on its cavity face, and acover was obtained by compression molding. The thickness of the coverwas 0.5 mm. Dimples having a shape that is the inverted shape of thepimples were formed on the cover.

A clear paint including a two-component curing type polyurethane as abase material was applied to this cover to obtain a golf ball of Example1 with a diameter of about 42.7 mm and a weight of about 45.6 g. Dimplespecifications I of the golf ball are shown in detail in Tables 4, 6,and 8 below. FIG. 2 is a plan view of the golf ball, and FIG. 3 is afront view of the golf ball.

Examples 2 and 3 and Comparative Examples 1 to 4

Golf balls of Examples 2 and 3 and Comparative Examples 1 to 4 wereobtained in the same manner as Example 1, except the specifications ofthe dimples were as shown in Tables 10 and 11 below. The specificationsof the dimples are shown in detail in Tables 4 to 9 below.

Examples 4 to 8

Golf balls of Examples 4 to 8 were obtained in the same manner asExample 1, except the specifications of the core, the mid layer, and thecover were as shown in Table 12 below. The specifications of the coreare shown in detail in Table 1 below. The specifications of the midlayer are shown in detail in Table 2 below. The specifications of thecover are shown in detail in Table 3 below.

Comparative Examples 5 to 11

Golf balls of Comparative Examples 5 to 11 were obtained in the samemanner as Example 1, except the specifications of the core, the midlayer, the cover, and the dimples were as shown in Tables 13 and 14below. The specifications of the core are shown in detail in Table 1below. The specifications of the mid layer are shown in detail in Table2 below. The specifications of the cover are shown in detail in Table 3below. The specifications of the dimples are shown in detail in Tables 4to 9 below.

Example 9

A rubber composition A was obtained by kneading 100 parts by weight of ahigh-cis polybutadiene (the aforementioned “BR-730”), 35 parts by weightof magnesium acrylate, 28 parts by weight of methacrylic acid, anappropriate amount of barium sulfate, and 1.3 parts by weight of dicumylperoxide. The rubber composition A was placed into a mold includingupper and lower mold halves each having a hemispherical cavity, andheated at 160° C. for 20 minutes to obtain a center with a diameter of15.0 mm. The amount of barium sulfate was adjusted such that a centerhaving a predetermined weight was obtained.

A rubber composition C was obtained by kneading 100 parts by weight of ahigh-cis polybutadiene (the aforementioned “BR-730”), 33.0 parts byweight of zinc diacrylate, 5 parts by weight of zinc oxide, anappropriate amount of barium sulfate, 0.9 parts by weight of dicumylperoxide, and 0.3 parts by weight of pentabromo diphenyl disulfide. Halfshells were formed from the rubber composition C. The center was coveredwith two of the half shells. The center and the half shells were placedinto a mold including upper and lower mold halves each having ahemispherical cavity, and heated at 160° C. for 20 minutes to obtain acore with a diameter of 39.7 mm. The amount of barium sulfate wasadjusted such that a core having a predetermined weight was obtained.

A resin composition M1 was obtained by kneading 47 parts by weight of anionomer resin (the aforementioned “Himilan 1605”), 50 parts by weight ofanother ionomer resin (the aforementioned “Himilan AM7329”), 3 parts byweight of a styrene block-containing thermoplastic elastomer (theaforementioned “RABALON T3221C”), and 4 parts by weight of titaniumdioxide with a twin-screw kneading extruder. The core was covered withthe resin composition M1 by injection molding to form a mid layer with athickness of 1.0 mm.

A paint composition (trade name “POLIN 750LE”, manufactured by SHINTOPAINT CO., LTD.) including a two-component curing type epoxy resin as abase polymer was prepared. The base material liquid of this paintcomposition includes 30 parts by weight of a bisphenol A type epoxyresin and 70 parts by weight of a solvent. The curing agent liquid ofthis paint composition includes 40 parts by weight of a modifiedpolyamide amine, 55 parts by weight of a solvent, and 5 parts by weightof titanium dioxide. The weight ratio of the base material liquid to thecuring agent liquid is 1/1. This paint composition was applied to thesurface of the mid layer with a spray gun, and kept at 23° C. for 12hours to obtain a reinforcing layer with a thickness of 10 μm.

A resin composition C1 was obtained by kneading 100 parts by weight of athermoplastic polyurethane elastomer (the aforementioned “ElastollanNY80A”), 0.2 parts by weight of a light stabilizer (trade name “TINUVIN770”), and 4 parts by weight of titanium dioxide with a twin-screwkneading extruder. Half shells were obtained from the resin compositionC1 by compression molding. The sphere consisting of the core, the midlayer, and the reinforcing layer was covered with two of these halfshells. These half shells and the sphere were placed into a final moldthat includes upper and lower mold halves each having a hemisphericalcavity and having a large number of pimples on its cavity face, and acover was obtained by compression molding. The thickness of the coverwas 0.5 mm. Dimples having a shape that is the inverted shape of thepimples were formed on the cover.

A clear paint including a two-component curing type polyurethane as abase material was applied to this cover to obtain a golf ball of Example9 with a diameter of about 42.7 mm and a weight of about 45.6 g. Dimplespecifications I of the golf ball are shown in detail in Tables 4, 6,and 8 below.

Comparative Example 12

A golf ball of Comparative Example 12 was obtained in the same manner asExample 9, except the specifications of the dimples were as shown inTable 14 below. The specifications of the dimples are shown in detail inTables 5, 7, and 9 below.

[Flight Test]

A driver (trade name “SRIXON Z-TX”, manufactured by DUNLOP SPORTS CO.LTD., shaft hardness: X, loft angle: 8.5°) was attached to a swingmachine manufactured by Golf Laboratories, Inc. A golf ball was hitunder a condition of a head speed of 50 m/sec, and the ball speed, thespin rate, and the flight distance were measured. The flight distance isthe distance between the point at the hit and the point at which theball stopped. The average value of data obtained from 12 measurements isshown in Tables 10 to 14 below.

[Controllability]

A sand wedge (trade name “XXIO”, manufactured by DUNLOP SPORTS CO. LTD.,shaft hardness: R, loft angle: 56°) was attached to a swing machinemanufactured by Golf Laboratories, Inc. A golf ball was hit under acondition of a head speed of 21 m/sec, and the spin rate was measured.The average value of data obtained from 12 measurements is shown inTables 10 to 14 below.

TABLE 1 Composition of Core (parts by weight) A B C Polybutadiene 100  100 100 Zinc diacrylate — 29.5 33.0 Magnesium acrylate 35.0 — —Methacrylic acid 28.0 — — Zinc oxide — 5 5 Barium sulfate AppropriateAppropriate Appropriate amount amount amount Dicumyl peroxide  1.3 0.90.9 Pentabromo diphenyl — 0.3 0.3 disulfide 2-naphthalenethiol — 0.1 —Benzoic acid — 2.0 —

TABLE 2 Composition of Mid Layer (parts by weight) M1 M2 M3 M4 Surlyn8150 — 50 — — Himilan 1605 47 — — — Himilan AM7329 50 50 — — HimilanAM7337 — — — 26 Himilan 1555 — — 47 40 Himilan 1557 — — 46 — RABALONT3221C  3 — 7 34 Titanium dioxide  4  4 4  4 Hardness Hm (Shore D) 63 6857 43 Hardness (Shore C) 91 94 86 70

TABLE 3 Composition of Cover (parts by weight) C1 C2 C3 C4 ElastollanNY80A 100 — — — Elastollan NY84A — 100 — — Elastollan NY88A — — 100 —Himilan 1605 — — — 47 Himilan AM7329 — — — 50 RABALON T3221C — — — 3TINUVIN 770 0.2 0.2 0.2 0.2 Titanium dioxide 4 4 4 4 Hardness Hc (ShoreD) 27 31 36 63

TABLE 4 Specifications of Dimples Dm Dp2 Dp1 CR V Number (mm) (mm) (mm)(mm) (mm³) I A 60 4.40 0.138 0.2506 17.61 1.051 B 158 4.30 0.137 0.244516.94 0.996 C 72 4.15 0.134 0.2341 16.13 0.908 D 36 3.90 0.123 0.211415.52 0.736 E 12 3.00 0.122 0.1743 9.28 0.432 II A 30 4.60 0.135 0.258119.66 1.123 B 66 4.50 0.135 0.2528 18.82 1.075 C 84 4.40 0.135 0.247617.99 1.028 D 30 4.30 0.135 0.2425 17.19 0.982 E 48 4.20 0.135 0.237616.40 0.936 F 60 4.00 0.135 0.2280 14.88 0.850 G 6 2.70 0.135 0.17736.82 0.388 III A 6 4.70 0.135 0.2635 20.52 1.172 B 126 4.40 0.135 0.247617.99 1.028 C 122 4.30 0.135 0.2425 17.19 0.982 D 6 4.15 0.135 0.235116.01 0.914 E 66 3.90 0.135 0.2234 14.15 0.808 F 12 3.00 0.135 0.18738.40 0.478

TABLE 5 Specifications of Dimples Dm Dp2 Dp1 CR V Number (mm) (mm) (mm)(mm) (mm³) IV A 30 4.60 0.135 0.2581 19.66 1.123 B 68 4.50 0.135 0.252818.82 1.075 C 92 4.40 0.135 0.2476 17.99 1.028 D 74 4.30 0.135 0.242517.19 0.982 E 38 4.15 0.135 0.2351 16.01 0.914 F 14 3.85 0.135 0.221113.79 0.787 G 8 3.60 0.135 0.2103 12.07 0.688 V A 156 4.91 0.135 0.276622.39 2.609 B 98 4.65 0.135 0.2620 20.09 2.217 C 12 3.00 0.135 0.18788.40 0.663 VI A 70 4.10 0.135 0.2336 15.63 1.538 B 30 3.90 0.135 0.224214.15 1.336 C 120 3.80 0.135 0.2197 13.44 1.243 D 170 3.70 0.135 0.215312.74 1.155 E 20 3.60 0.135 0.2110 12.07 1.072 F 12 2.50 0.135 0.17165.85 0.422 VII A 30 4.60 0.135 0.2581 19.66 1.123 B 54 4.50 0.135 0.252818.82 1.075 C 72 4.30 0.135 0.2425 17.19 0.982 D 54 4.20 0.135 0.237616.40 0.936 E 108 4.00 0.135 0.2280 14.88 0.850 F 12 2.70 0.135 0.17736.82 0.388

TABLE 6 Aerodynamic Characteristic I II III Peak Pd1 270.2 143.5 195.1value Pd2 177.9 195.4 153.1 Pd3 150.2 147.0 147.8 Pd4 316.4 322.0 322.0Pd5 190.0 152.2 152.2 Pd6 270.2 143.5 195.1 Pd7 177.9 195.4 153.1 Pd8150.2 147.0 147.8 Pd9 316.4 322.0 322.0 Pd10 190.0 152.2 152.2 Pd11270.2 143.5 195.1 Pd12 177.9 195.4 153.1 Pd13 150.2 147.0 147.8 Pd14316.4 322.0 322.0 Pd15 190.0 152.2 152.2 Order Fd1 33 31 31 Fd2 37 31 31Fd3 37 33 33 Fd4 34 36 36 Fd5 27 29 29 Fd6 33 31 31 Fd7 37 31 31 Fd8 3733 33 Fd9 34 36 36 Fd10 27 29 29 Fd11 33 31 31 Fd12 37 31 31 Fd13 37 3333 Fd14 34 36 36 Fd15 27 29 29

TABLE 7 Aerodynamic Characteristic IV V VI VII Peak Pd1 116.0 245.2181.3 206.0 value Pd2 93.2 204.6 117.2 302.6 Pd3 174.6 317.5 87.3 190.4Pd4 440.9 336.5 296.0 420.1 Pd5 151.1 134.7 146.3 112.6 Pd6 207.7 147.7225.3 196.5 Pd7 177.0 230.7 329.8 155.2 Pd8 165.9 458.1 347.1 281.5 Pd9257.7 778.5 259.2 358.3 Pd10 157.5 244.8 165.7 89.7 Pd11 187.0 524.8181.3 206.0 Pd12 146.3 284.0 117.2 302.6 Pd13 263.3 184.0 87.3 190.4Pd14 383.1 282.7 296.0 420.1 Pd15 146.1 185.4 146.3 112.6 Order Fd1 3125 35 31 Fd2 33 29 37 33 Fd3 30 29 35 29 Fd4 34 31 41 31 Fd5 32 31 35 29Fd6 30 33 39 35 Fd7 33 31 37 37 Fd8 34 29 39 31 Fd9 34 31 41 33 Fd10 3029 35 33 Fd11 31 29 35 31 Fd12 32 23 37 33 Fd13 32 29 35 29 Fd14 34 3141 31 Fd15 32 31 35 29

TABLE 8 Specifications of Dimples I II III Front view FIG. 2 FIG. 25FIG. 27 Plan view FIG. 3 FIG. 26 FIG. 28 Total number N 338 324 338Total volume TV (mm³) 564.6 579.0 574.3 Peak value Max 316.4 322.0 322.0Pd Min 150.2 143.5 147.8 Ave 220.9 192.0 194.0 Order Max 37 36 36 Fd Min27 29 29 Ave 33.6 32.0 32.0

TABLE 9 Specifications of Dimples IV V VI VII Front view FIG. 29 FIG. 31FIG. 33 FIG. 35 Plan view FIG. 30 FIG. 32 FIG. 34 FIG. 36 Total number N324 266 422 330 Total volume TV (mm³) 589.7 632.2 519.8 571.3 Peak valueMax 440.9 778.5 347.1 420.1 Pd Min 93.2 134.7 87.3 89.7 Ave 204.5 304.0198.9 236.3 Order Max 34 33 41 37 Fd Min 30 23 34 29 Ave 32.1 29.4 37.131.7

TABLE 10 Results of Evaluation Ex. 1 Ex. 2 Ex. 3 Core (center) B B BDiameter (mm) 39.7 39.7 39.7 Envelope layer — — — Ho (Shore C) 54 54 54Hs (Shore C) 80 80 80 Mid layer M1 M1 M1 Hardness Hmc (Shore C) 93 93 93Hardness Hm (Shore D) 63 63 63 Thickness Tm (mm) 1.0 1.0 1.0 Cover C1 C1C1 Hardness Hc (Shore D) 27 27 27 Thickness Tc (mm) 0.5 0.5 0.5 Dimple III III Hmc − Hs 13 13 13 Hm − Hc 36 36 36 Compression Sb (mm) 2.8 2.82.8 V1 121 121 121 V2 0.823 0.823 0.823 W1 ball speed (m/s) 73.3 73.373.3 W1 spin rate (rpm) 2650 2650 2650 W1 flight distance (m) 263.7262.6 263.1 SW spin rate (rpm) 6520 6520 6520

TABLE 11 Results of Evaluation Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3Ex. 4 Core (center) B B B B Diameter (mm) 39.7 39.7 39.7 39.7 Envelopelayer — — — — Ho (Shore C) 54 54 54 54 Hs (Shore C) 80 80 80 80 Midlayer M1 M1 M1 M1 Hardness Hmc (Shore C) 93 93 93 93 Hardness Hm (ShoreD) 63 63 63 63 Thickness Tm (mm) 1.0 1.0 1.0 1.0 Cover C1 C1 C1 C1Hardness Hc (Shore D) 27 27 27 27 Thickness Tc (mm) 0.5 0.5 0.5 0.5Dimple IV V VI VII Hmc − Hs 13 13 13 13 Hm − Hc 36 36 36 36 CompressionSb (mm) 2.8 2.8 2.8 2.8 V1 121 121 121 121 V2 0.823 0.823 0.823 0.823 W1ball speed (m/s) 73.3 73.3 73.3 73.3 W1 spin rate (rpm) 2650 2650 26502650 W1 flight distance (m) 261.3 261.0 260.9 260.8 SW spin rate (rpm)6520 6520 6520 6520

TABLE 12 Results of Evaluation Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Core(center) B B B B B Diameter (mm) 39.7 39.7 39.7 39.7 39.7 Envelope layer— — — — — Ho (Shore C) 54 54 54 54 54 Hs (Shore C) 80 80 80 80 80 Midlayer M2 M3 M1 M2 M1 Hardness Hmc (Shore C) 98 86 93 98 93 Hardness Hm(Shore D) 68 57 63 68 63 Thickness Tm (mm) 1.0 1.0 1.0 1.0 1.0 Cover C1C1 C2 C2 C3 Hardness Hc (Shore D) 27 27 31 31 36 Thickness Tc (mm) 0.50.5 0.5 0.5 0.5 Dimple I I I I I Hmc − Hs 18 6 13 18 13 Hm − Hc 41 30 3237 27 Compression Sb (mm) 2.7 2.9 2.8 2.7 2.8 V1 131 110 106 114 91 V20.735 0.942 0.717 0.640 0.617 W1 ball speed (m/s) 73.3 73.2 73.3 73.473.4 W1 spin rate (rpm) 2610 2680 2620 2580 2550 W1 flight distance (m)264.1 263.0 263.9 265.0 265.3 SW spin rate (rpm) 6400 6580 6450 63806340

TABLE 13 Results of Evaluation Comp. Comp. Comp. Comp. Ex. 5 Ex. 6 Ex. 7Ex. 8 Core (center) B B B B Diameter (mm) 39.7 39.7 39.7 39.7 Envelopelayer — — — — Ho (Shore C) 54 54 54 54 Hs (Shore C) 80 80 80 80 Midlayer M2 M3 M1 M2 Hardness Hmc (Shore C) 98 86 93 98 Hardness Hm (ShoreD) 68 57 63 68 Thickness Tm (mm) 1.0 1.0 1.0 1.0 Cover C1 C1 C2 C2Hardness Hc (Shore D) 27 27 31 31 Thickness Tc (mm) 0.5 0.5 0.5 0.5Dimple IV IV IV IV Hmc − Hs 18 6 13 18 Hm − Hc 41 30 32 37 CompressionSb (mm) 2.7 2.9 2.8 2.7 V1 131 110 106 114 V2 0.735 0.942 0.717 0.640 W1ball speed (m/s) 73.3 73.2 73.3 73.4 W1 spin rate (rpm) 2610 2680 26202580 W1 flight distance (m) 261.7 260.5 261.5 262.4 SW spin rate (rpm)6400 6580 6450 6380

TABLE 14 Results of Evaluation Comp. Comp. Comp. Comp. Ex. 9 Ex. 10 Ex.11 Ex. 9 Ex. 12 Core (center) B B B A A Diameter (mm) 39.7 39.7 39.715.0 15.0 Envelope layer — — — C C Ho (Shore C) 54 54 54 60 60 Hs (ShoreC) 80 80 80 86 86 Mid layer M3 M4 M4 M1 M1 Hardness Hmc (Shore C) 86 7070 93 93 Hardness Hm (Shore D) 57 43 43 63 63 Thickness Tm (mm) 1.0 1.01.0 1.0 1.0 Cover C4 C1 C4 C1 C1 Hardness Hc (Shore D) 63 27 63 27 27Thickness Tc (mm) 0.5 0.5 0.5 0.5 0.5 Dimple I I I I IV Hmc − Hs 6 −10−10 7 7 Hm − Hc −6 16 −20 36 36 Compression Sb (mm) 2.8 2.9 2.8 2.4 2.4V1 47 83 35 121 121 V2 0.390 1.249 0.517 0.705 0.705 W1 ball speed (m/s)73.3 73.2 73.3 73.5 73.5 W1 spin rate (rpm) 2560 2780 2660 2700 2700 W1flight distance (m) 264.2 261.9 263.2 264.2 261.8 SW spin rate (rpm)5800 6600 5830 6620 6620

As shown in Tables 10 to 14, the golf ball of each Example has excellentflight performance upon a shot with a driver and excellentcontrollability upon an approach shot. From the results of evaluation,advantages of the present invention are clear.

The golf ball according to the present invention is suitable for, forexample, playing golf on golf courses and practicing at driving ranges.The above descriptions are merely illustrative examples, and variousmodifications can be made without departing from the principles of thepresent invention.

What is claimed is:
 1. A golf ball comprising a core, a mid layerpositioned outside the core, and a cover positioned outside the midlayer, wherein a Shore C hardness Hmc of the mid layer is greater than aShore C hardness Hs at a surface of the core, a Shore D hardness He ofthe cover is less than a Shore D hardness Hm of the mid layer, the golfball further comprises a plurality of dimples on a surface thereof, aminimum value of 15 peak values obtained by executing steps (a) to (h)for each of 15 axes Ax is not less than 95 mm, when spherical polarcoordinates of a point that is located on a surface of a phantom sphereof the golf ball and has a latitude of 9 (degrees) and a longitude of ϕ(degrees) are represented by (θ, ϕ), the 15 axes Ax being (1) a firstaxis Ax1 passing through a point Pn1 coordinates of which are (75, 270)and a point Ps1 coordinates of which are (−75, 90), (2) a second axisAx2 passing through a point Pn2 coordinates of which are (60, 270) and apoint Ps2 coordinates of which are (−60, 90) (3) a third axis Ax3passing through a point Pn3 coordinates of which are (45, 270) and apoint Ps3 coordinates of which are (−45, 90), (4) a fourth axis Ax4passing through a point Pn4 coordinates of which are (30, 270) and apoint Ps4 coordinates of which are (−30, 90), (5) a fifth axis Ax5passing through a point Pn5 coordinates of which are (15, 270) and apoint Ps5 coordinates of which are (−15, 90), (6) a sixth axis Ax6passing through a point Pn6 coordinates of which are (75, 0) and a pointPs6 coordinates of which are (−75, 180), (7) a seventh axis Ax7 passingthrough a point Pn7 coordinates of which are (60, 0) and a point Ps7coordinates of which are (−60, 180), (8) an eighth axis Ax8 passingthrough a point Pn8 coordinates of which are (45, 0) and a point Ps8coordinates of which are (−45, 180), (9) a ninth axis Ax9 passingthrough a point Pn9 coordinates of which are (30, 0) and a point Ps9coordinates of which are (−30, 180), (10) a tenth axis Ax10 passingthrough a point Pn10 coordinates of which are (15, 0) and a point Ps10coordinates of which are (−15, 180), (11) an eleventh axis Ax11 passingthrough a point Pn11 coordinates of which are (75, 90) and a point Ps11coordinates of which are (−75, 270), (12) a twelfth axis Ax12 passingthrough a point Pn12 coordinates of which are (60, 90) and a point Ps12coordinates of which are (−60, 270), (13) a thirteenth axis Ax13 passingthrough a point Pn13 coordinates of which are (45, 90) and a point Ps13coordinates of which are (−45, 270), (14) a fourteenth axis Ax14 passingthrough a point Pn14 coordinates of which are (30, 90) and a point Ps14coordinates of which are (−30, 270), and (15) a fifteenth axis Ax15passing through a point Pn15 coordinates of which are (15, 90) and apoint Ps15 coordinates of which are (−15, 270), the steps (a) to (h)being the steps of (a) assuming a great circle that is present on thesurface of the phantom sphere and is orthogonal to the axis Ax, (b)assuming two small circles that are present on the surface of thephantom sphere, that are orthogonal to the axis Ax, and of whichabsolute values of central angles with the great circle are each 30°,(c) defining a region, of the surface of the golf ball, which isobtained by dividing the surface of the golf ball at these small circlesand which is sandwiched between these small circles, (d) determining30240 points, on the region, arranged at intervals of a central angle of3° in a direction of the axis Ax and at intervals of a central angle of0.25° in a direction of rotation about the axis Ax, (e) calculating alength L1 of a perpendicular line that extends from each point to theaxis Ax, (f) calculating a total length L2 by summing 21 lengths L1calculated on the basis of 21 perpendicular lines arranged in thedirection of the axis Ax, (g) obtaining a transformed data constellationby performing Fourier transformation on a data constellation of 1440total lengths L2 calculated along the direction of rotation about theaxis Ax, and (h) calculating a peak value and an order of a maximum peakof the transformed data constellation, a minimum value of 15 ordersobtained by executing the steps (a) to (h) is not less than 27, amaximum value of the 15 orders obtained by executing the steps (a) to(h) is not greater than 37, and an average of the 15 orders obtained byexecuting the steps (a) to (h) is not less than 30 and not greater than34.
 2. The golf ball according to claim 11, wherein an average of the 15peak values obtained by executing the steps (a) to (h) is not less than200 mm.
 3. The golf ball according to claim 1, wherein a total volume ofthe dimples is not less than 450 mm³ and not greater than 750 mm³. 4.The golf ball according to claim 1, wherein a difference DH in Shore Chardness between the surface and a central point of the core, athickness Tm (mm) and the Shore D hardness Hm of the mid layer, athickness Tc (mm) and the Shore D hardness He of the cover, and anamount of compressive deformation Sb (mm) of the golf ball satisfy thefollowing mathematical formulas (i) and (ii),(DH*Hm)/(Hc*Tc)>90  (i), and((Sb*Tc)/(Hc*Hm*Tm))*1000>0.60  (ii).
 5. The golf ball according toclaim 1, wherein a difference (Hmc−Hs) between the Shore C hardness Hmcof the mid layer and the Shore C hardness Hs at the surface of the coreis not less than
 5. 6. The golf ball according to claim 1, wherein adifference (Hm−Hc) between the Shore D hardness Hm of the mid layer andthe Shore D hardness He of the cover is not less than 20.